much to my surprise this info states stay away from the 906 vortec heads.
this is a great article
QUOTE The easiest way to identify a Vortec head is by the sawtooth pattern cast into the front. Look for casting number 12558062, but avoid casting number 10239906, which has a modified exhaust seat and loses 20 percent of its flow at 0.120-inch lift. QUOTE

http://www.chevyhiperformance.com/howto/97458/

AS I FIND MORE INFO IT WILL BE ADDED

FEEL FREE TO ADD ANY INFO YOU MAY FIND

HERES HOW TO TELL THEM APART.

the chambers are heart shaped.
the saw tooth on the head ends.
center bolt valve covers.
only 4 (four) intake bolts.

THE ONES YOU WANT..if your not buying aftermarket are 062 heads.
the 906's have a different exhaust valve seat that lowers the flow. ? as stated by above article. gilbert chevy say's no?

10239906 casting has one large single hump.
12558062 casting has 3 small humps.

heres the steam holes drilled for use with a 400 engine

i drilled them my self.

the way to tell a 062 or 906 is to look under the valve cover or flip the head over and see the casting number...

IF YOUR LOOKING TO TELL THE DIFFERENCE BETWEEN 062'S AND 906'S BY LOOKING AT THE HEAD END.
10239906 casting has one large single hump.
12558062 casting has 3 small humps.

I WOULD LOVE TO HAVE A SET OF 060'S

tech info: REWORKED HEADS FROM GMPP

Part Number: 12558060
Description: L31 with valves
Material: Cast Iron
Head Bolt Torque: 65 ft./lbs.
Valvespring Seat: 1.300” O.D., 0.850” I.D.
Valve-guide Seals: Viton rubber positive seals, total 0.450” retainer-to-seal clearance Combustion Chamber Volume: 64 cc
Spark Plugs: Straight
Heat Risers: No
Valvesprings: Single wire with damper 1.235” O.D., 0.875” I.D. 75-pound seat pressure @ 1.700” installed height Coil-bind @ 1.150”
Intake Bolt Pattern: Four bolts per side
Rocker Arm Style: Self-Aligning Intake Runner Volume: 170 cc
Valve Diameter: I: 1.94”, E: 1.50”
Casting Numbers: 10239906 and 12558062
Max. Valve Lift: 0.420” which allows 0.030” retainer-to-seal
Rocker Stud: Press-in, 3/8” diameter
Spark-plug Style: 14 mm, ¾ reach, tapered seat
Notes: LT1 Design Port with valves and springs.

HERE'S WHAT GILBERT CHEVY SAY'S ABOUT THE TWO DIFFERENT VORTEC HEADS.?
Please Note: The casting number myth debunked:
The myth is that there is a difference in the head performance produced by these two castings.
This myth was started by some Magazines that didn't do their homework before publishing their articles.
This is the truth the whole truth and nothing but the truth. So sayith the Grand Wizard GM and his Apprentice Wizard GILBERT CHEVROLET.
10239906 casting has one large single hump.
12558062 casting has 3 small humps.
If either of these two castings have not been altered by GM and the part number changed from 12558060 or altered by someone else (previous owner, etc.), the heads produced by either casting will be identical except for the external cosmetic difference. Both castings are used to make the 12558060 Vortec heads which are the true unaltered Vortec heads.
Heads from both castings come out of their cast IDENTICAL except for the minor cosmetic external differences!!!!!!!!

Special Spark Plugs For The Vortec Heads
R44LTSM, set of 8
MR43LTS, set of 8
P526S Accel U-Groove “SHORTY” Double Platinum Header Plugs approximately 3/16" shorter then R44LTS plugs, set of 8

heres a picture of some guys ported and polished vortec heads

one of mine untouched

http://members.cox.net/dnjunk/vortec%20222.jpg

HERE'S WHAT GILBERT CHEVY SAY'S ABOUT THE TWO DIFFERENT VORTEC HEADS.?
Please Note: The casting number myth debunked:
The myth is that there is a difference in the head performance produced by these two castings.
This myth was started by some Magazines that didn't do their homework before publishing their articles.
This is the truth the whole truth and nothing but the truth. So sayith the Grand Wizard GM and his Apprentice Wizard GILBERT CHEVROLET.
10239906 casting has one large single hump.
12558062 casting has 3 small humps.
If either of these two castings have not been altered by GM and the part number changed from 12558060 or altered by someone else (previous owner, etc.), the heads produced by either casting will be identical except for the external cosmetic difference. Both castings are used to make the 12558060 Vortec heads which are the true unaltered Vortec heads.
Heads from both castings come out of their cast IDENTICAL except for the minor cosmetic external differences!!!!!!!!

The 906 castings used for 1996-99 CK heavy-duty truck applications had single-angle Iconel seats vs. the induction-hardened three-angle seats in other application and GMPP heads. Agreed that the casting is the same, but the seats are clearly not...and this was the core of Car Craft's contention that the single-angle seats a significant impact on flow. Also agreed that there's no reason to shy away from the 906 casting...just some careful checking when buying used or junking for a set of these.

figured i better show some pictures of the different rockers used on late model gm heads that require self aligning rockers. vortec heads require these.
just for a FYI.
the first two pictures are a self aligning rocker..
the third is a regular style
the last both side by side

Side note as stated above the castings are the same the seats are different.
Any one planning to have their vortec heads machined to accept 2.02 1.06 valves need not worry witch casting # they may start with. Also as an added note the self aligning rockers need to be used unless you would install guide plates as rage'nrat638 did on his vortec heads on another thread. :metal: