If you were to check, you'd find that the grade 8 bolt doesn't have the same head style as the flywheel bolt (it's called a "place bolt,") but I think you can change the clutch retaining bolts without too much trouble - use SHCS for those (since they're nearly as strong as SAE Grade 8 as a rule, but are a little softer and can handle shear stress better.)
The "place bolt" usually has a small undercut on the head that allows for flexion of the bolt head, as well as a "spring load" on the retained part - which is something that shouldn't be done away with. Also, once you machine or grind down the SAE Grade 8, you lose the rust protection you get from the chrome or zinc chromate plating - a bad thing.
I know the threads are 1/2"-20 - can you tell me the underhead length on your bolts? I'll go through ARP for a set that can match up - if you're going to have to spend a few bucks, might as well do it right. I can work on the same thing for the clutch retaining bolts as well - I'm reasonably sure they're 3/8"-16 (please check,) but I don't know the lengths...
5-90