['63GENIII]

Try giving a call to Chris Straub. Im running one of his cams that was designed for the SS 454 engine. IIRC, it was dynoed at something like 450 / 525 in the TBI combo (which I think was a lower compression engine too). Im running this cam in my L29 (with the Vortec heads) and it pulls like a freight train on the "slightly" hotter than stock tune which just eliminated the EGR, rear o2 sensor and gave it fuel and timing maps to work with the rest of the truck.

Non adjustable valve train completely sucks so if you have your heads off for any reason... get them drilled and tapped for the standard BBC 7/16 studs. Don't believe the BS about the Comp Cams conversion studs. They are crap and you can't find 3/8" guide plates to use with their studs anymore.

For using Vortec heads on the older block -

I think that if you have the 1 piece rear seal, you should be fine.

2 piece rear seal requires a slightly different head gasket to be sealed up right.

1 piece rear seal is likely machined for a roller cam retainer plate. This is good. Take advantage of it.

Vortec heads are fine but there is just not a lot of real hard info on them. They were kind of like a GM experiment until the big cathedral port 8.1 came along.

The Vortecs don't respond too well to porting unless you like water injection and the intakes really could use porting due to the ski jump in them.

Once in the chamber, there is the heart shape cast into the chamber that is supposed to promote complete ignition of the mixture. The casting comes to such a sharp point that it will actually slice your hands open if not careful. I looked at this point as a possible source of detonation. This could be why the Vortecs are tune limited to 30 deg. total advance. Exhaust is a different story. The D shaped ports flow fairly well and don't need much work to work well on the street. All in all though, these heads are done at 5,000 - 5,500.