With a stock cam, and a full port polish you would probably see around 10-13 hp gain at the flywheel.
If you just port the lower intake, you would be looking at like 3-7 power gain
With the 422 cam you would see those numbers probably double.
Stage two you could use the 410 cam with
Stage three you could use the 422 cam.
With just those heads, and new rings, you would be in the 170-175 hp range
Add in 410 cam, you would be around the 185-190 hp range
Use 422 cam you would be at or a little above 200 hp
Use 95TM/97TM/98TM style castings with your 91 style pistons and you will up the compression to 10:1, or you can use SOHC pistons with the 90TM/93TM style heads for the 10:1 compression... 210-220 hp range (theoretically, I haven’t finished my build to dyno this setup yet) You would officially have the mean 4.0, although 93 octane or higher would be mandatory.
A lot of people use SuperSix, quality work. I hate to brag, but i bought my stage III ported heads for a 1/4 that cost
