i have a 86 z-28 with 350 built and procharged with a tremec tko 5 speed and a broke down 10 bolt 7.5. will a built 10 bolt 8.5 hold that power and if so will the wheels stick out far from the car

it all depends. Every tranny is different. I have seen some people with there stock 10 bolts run 11's. A 8.5 should be fine though for awhile

For the cost of getting a 8.5" 10-bolt under the car, plus the cost of building it up to take decent power, it's not likely to be worth it. You'll have almost, if not as much, into doing so as just swapping to a bolt-in 12-bolt. Obviously, a mild 12-bolt will handle that and then some if you want to build it up.

an 8.5 is not a bolt-in. It's a custom, one-off conversion.