What are guys running there base timing at with a comp roller 270 marine cam

That's kind of a loaded question.....there's a lot that goes into setting the timing of an engine. Lets' start off by asking you what heads are you running?

Vortec edelbrock carb and rpm intake 9.5 compression with stainless marine exhaust

I think a better question would be what totl timing as TBolt IV distributors can't change the timng curve. That said, 30-32 total will be good. Double check at 4k to make sure your module isn't advancing still.

With a typical 24* module this will leave you at 8-10 initial. But always check/adjust by total just in case as that's more importnat.

If you have an adjustable timing curve distributor, anywhere between 12-16 initial will be fine, with again 30-32 total. All in by 3k-3500rpm is fine.

I'm at 8 BTDC base timing but using timing table on a MEFI 1 unit. 33-34 degrees total at peaks in the table. Crower roller cam sorta similar to the Comp 270.

If the bottom end is stock go 32 degrees total. If you have good squish and good pistons you can go maybe 34. If it has the better squish and pistons it will pull more rpms.