Have some questions.

I have the HiPo 360's had the 340 cam (not 6-pack)

Same cam. There was basicly 2, 340 cams. The second one being a slightly hotter one than what is normaly listed.

MPP suggests a 750 carb for their crate engines, which made me curious if I should go with the bigger carb.

If your racing it, it may produce 2-5 HP more at best. It is best used with a numerically larger gear ratio. 4.30's and up in a lightened car. It's alot of carb.

I wanted to stay as close to 9.5:1 CR so I can run lower octane if I wanted (it's actually is 9.6),

Good, stay right there. Thats about max for the street, cam dependent. (Larger cams bleed of cyl. pressure.)

the the origional pistons were so far in the bore I needed a flashlight to see them. But the 360 +.030 over (.010 shy of the 340 and bigger stroke) should have more grunt than the 340.

OH, it will, it will.