My guess is not much. OSAC started in '73 and I don't think any other major changes came along in '75 that would further effect timing, maybe the cat.
Do you have the book for '75? That will give you half the answer. In the back the of the electrical section, but prob before the wiring diagrams, will be the timing specs. Take a picture of that.
After its running, and see what you got, maybe we can make it peppy, or perky or something. ;)
I have an idea...