if you are goign to do anything with the 305..
get a camshaft.. they first one have/were natorious to flat cams due to their soft make up.
yes those head will work.. but hte major problem is this.
stock 305 heads come wiht a 58cc chamber.. the smalled 350 is a 64 oem.. most stock 305 run betwene 8-8.5:1 c/r wiht a 58cc head.. going to a 64 head will drop your comrpession below 8 which kill what little power you have.
if your dead set on building a 305.. heads are a good investment. OEM suck big time!!!! 300hp out of a 9.5:1 305 pretty easy. andyou have a very square motor.
i have used these on a 305
http://www.summitracing.com/parts/WRL-042650/http://www.worldcastings.com/products/s-r-stock-replacement-iron-heads.htmlHead Flow @ .500 Lift
220 intake, 151 exhaust (Super Flow 1050)
232 intake, 161 exhaust (Super Flow 600)
All heads flowed with a standard .750" intake plate, without exhaust tube, and 28" of water.