i got a late 60's 307 that im putting a q-jet flowing around 550 and am putting long tube headers and 1.6 rollertip rockers for a weird (its a 307, cant get much weirder) mild build. the heads on it are mismatched though. Im thinking im gonna get some matching heads from a "salvage" yard (buddy of mine owns a classic car junk yard).  what heads would anyone recommend for this build. the engine is gonna be connected to a T5 and i want to run 87 octane.  

The 307 is a 283 with a 327 crank. The 3.874 bore can accommodate heads with up to 1 .94 intake and 1.5 exhaust valve. The big problem is chamber size which needs to stay fairly small to hold onto a decent compression ratio. Try to stay away from open chamber (72-76cc) 350 SMOG heads from 1972 thru 1986. These will kill any compression on a 307 and tend to be cracked anyway. There are lots of 283/307/305 heads from various years that will work see Mortec at http://www.mortec.com/castnum.htm for lists of casting numbers. Those from 74 thru 86 have hardened exhaust seats so they tolerate unleaded fuel AND they will accept your intake bolt pattern. Those from 87 thru 95 also have hardened exhaust seats but use the newer 72 degree bolt angle on the center intake bolts, this requires a matching intake. Vortecs, which you can use, require another unique intake. These type of "fast burn" chambered heads add about 40 horses with no other changes, so they represent technology worth incorporating. Similar heads with these heart or kidney shaped chambers can be found in the aftermarket plus these guys give you a choice of intake port and bolt patterns as well as spark plug type. The former choice could allow you to use other intake manifold choices besides GMPP's Vortec to carb.

Some of these 307 blocks will accept an eigth inch overbore (.125"). With a 3.25" crank you now have a 327. Sonic checking of the cylinder wall thickness will tell you if it's safe to bore that far on your block.

Bogie

I just pulled some 76cc 1.94x1.5 off of an '86 mercruiser v8...these chambers are the same size as the original heads so they'll run...plus they were free, not cracked, and hardened seats. Im not looking for a screaming 307...the thought is laughable. I just want a little power that the 250 l6 was missing. I just lapped in those new valves this afternoon. putting those heads on tomorrow. Should be a fun morning.  

have fun

bogie

Another option : I found a pair of 305 heads with the bigger valves ,home-ported them ,put in the L79 cam .Sure I have to run premium gas now , but with regular at $3.00 a gal , premium is only 10% more (30 cents) . I'm sure I'm getting more than 10% better performance in my 65 ElCamino .I'ts old school tech  307