Edelbrock performer and performer RPM usally work the best for mild build and good tq at low rpm.
Power glide and 373 is not going to add up to much top end speed. If you want to cruise at 70mph forget it. Power glide is great for race track. Not so happy on the street with 373.
What type of pistons. I ask because 75cc heads dont usally give you 9.5:1 in a 383. Unless its zero deck and flat top pistons.
I would start here.
United Engine & Machine Co. Incorporated