ok i did a 4.3 swap to 305 in my 89 chev swb it's runnin good but it surge's a bit no service light i put the computer in for the 305 when i did the swap the only thing i have on the 305 from the 4.3 is the throttle body.....but i'm wondering if the o2 sensor would do this because on the 4.3 it's in the exhaust by the cat and on the 305 it's in the manifold d.s...would that cause it to surge......thanks everyone...........oh and did complete tune up in case u ask

The Model 220 TBI castings are the same except one used on big blocks. The injectors in the TBI unit have different flow rates depending on which engine it is.

If you have the TBI that was on the 305 use it. If you don’t have the TBI that was on the 305 you need to get some injectors for a 305.

Here is a link with a little TBI injector information:
http://groups.msn.com/AutoTechsOnline/knownfixesforgm.msnw

Might not hurt to check and clean the idle air control valve either. They usually don't throw a code, and will cause a surge at idle.

well i found a realy good throttle body finaly,and i can't beleive how much more power gain i have on take off i didn't think there was that much difference between the 4.3 and the 305 throttle body,but what a world of difference..............

Glad to hear of your success, and thanks for the update.