I kind of think your 6.60 (1/8) should be faster in the 1/4 . I am at 10.40s and better for that sixty
Definitely I would go a 4.1 gear .
Heads ? your choice , at a 10.00 limit the 270 might be best bang for buck . If going to upgrade for faster may need bigger heads . If buying rockers you may as well buy 1.6s if reusing the cam you have to grab extra lift
2"headers will help . I run Dougs with exhaust to diff . I have to run mufflers and it is a street car .
Rear seat out in my 68 Satellite was about 40lbs or so

Tex