In order to get a head that will perform significantly better than the vortecs in your application, you will probably be spending ~$1500-$2000. Even then, you will probably only be looking at a ~30 hp difference assuming you will have a somewhat low lift cam. `
I had a vortec headed 355 (listed below) that ran awsome once I threw some gear at it. I originally had a 700R4 with a 2:73 rear gear. I switched to a 3.90 and noticed more of a performance difference than I did when I switched from a 30 year old stock 307 to the new 355. If you are going to keep your gear, I would recommend a 2200 stall at least. I had a 1900 at it was not enough with the 2:73 gears. With the 3.90's it was about perfect though.
xe268h cam (224 230 @.050 .477 .480 lift)
performer RPM intake
650 holley DP
1 5/8th inch headers
It got ~18 mpg on the highway.