I would build a solid 400 + cube(big as is practical) smallblock shortblock, run the heads you have and a single plane intake and the proper cam and see what happens! Then you could upgrade heads if you need to. There are a number of head options, but with some porting on the stockers, you might make your goal.
for rear suspension SS springs would work, but will require some good adjustable shocks to control them. Box the spring pads. I rolled mine over years ago