When I was planning on staying with my 350, I got the following recommendations from Kauffman Racing Equipment. The engine is originally a 2bbl, now with Edelbrock Performer RPM intake/cam/4bbl carb matched for the 350. Stock heads. Check out the KRE discussion board http://bbs.cartserver.com/bbs/a/8962/index.cgi

Here's the advice I received...

"As far as the gears go, I'd stick with a 3.73. This ratio is an excellent compromise between driveability and overall acceleration potential. With regard to cylinder heads, most D-port heads that have a combustion chamber small enough to keep the compression ratio up in your engine are all going to act about the same in terms of overall horsepower potential. Save a few bucks and stick with the heads you have, and do some work to those. Focus on the bowl area behind the heads of the valves. Remove all the casting flash, blend the short-turn radius on the intake runners, and work on reshaping the bowls to give a more contoured path for airflow. You can blend the intake runners, but don't polish them completely -- you need a little bit of a rough surface to help prevent fuel puddling. Maintain the overall exhaust runner shape, with a thorough blending and polishing. Finally, gasket match the intake to the cylinder heads, and don't forget a good valve job. You may consider upgrading to stainless steel valves, at least on the exhaust side. Usually, you can get away with running stainless valves without installing hardened seats for compatibility with today's unleaded fuels, assuming the seats aren't already damaged. Avoid larger valve packages -- the 2.11/1.77 valve combo is really too large for a basic 350 engine. These larger valves typically require notching the tops of the cylinder bores for clearance, as the 350 has a relatively small 3.875" cylinder bore diameter. Also, once you get the valves to clear, the typical gains in airflow provided by the larger valves are instantly negated by the excessive shrouding of the valves by the cylinder bores. These modifications coupled with the parts you've already obtained should make for a throttle responsive engine that is fun to drive. While you may not set the world on fire, it should make you smile when you hit the pedal, and the typical 5.0 Mustang that pulls up next to you at the red light really shouldn't be much of a challenge. As a side note on the transmission, consider the 200-4R for your 4-speed auto conversion. While not quite as beefy in stock form as a 700-R4, it can be built into quite a nice performance transmission. It already features the B.O.P. bellhousing bolt pattern, so you won't need any adapter plates. Also, if you're replacing a Powerglide or TH-350, the output shaft of the 200-4R is the same spline count, and very close to the same length, so your existing driveshaft should work with no problems. The crossmember may need to be slightly relocated, but tranny mounts are the same. Art Carr builds one of the nicest 200-4R transmissions out there. Don't forget a good transmission cooler, and appropriately sized cooler lines (3/8" hardline, or -6AN braided steel flex line). The other nice feature of the 200-4R is that it has a 2.74 first gear ratio versus the 700-R4 ratio of 3.06. While the 3.06 ratio provides better initial acceleration, the RPM drop between the 1-2 gear change is excessive, and will usually pull the engine out of it's powerband. Have fun!"