I agree with Bigwildgrin.A 3.73 or 4.10 would be good.If you beefed up a TH700-R4 with a 2400 stall,That would be good for both.But I've had very good luck with TH400/TH350's.They hold up to drag racing pretty well.
If I had a 350 vortec motor Id put:
1.More compression 9.6:1.You could probably get away with 10:1.On Premium.But a little less is safer.
2.More Cam like the 276HR XE cam from Comp. Cams or one step higher.
3.A good double roller timing chain is fine
4.Heads:Take them and Get screw in studs and guideplates installed,Mild port and polish,Bowl blend,3 angle valve job,Bigger springs.You could fit bigger valves.But you probably dont need them.
6.Performer rpm intake
7.Holley carb,or a get a demon