what angle should i set my engine on a high wing trainer. its a sc .75 with aprox 6ft wingspan

Is it an ARF or a kit? Usually the engine thurst angle is already factored in with the firewall construction process.

its a homebuilt as far as i know and the firewall has been damaged in a crash an i am in the process of rebuilding

Two or three degrees of right thrust and two or three degrees of down thrust is pretty typical. I'd glue the firewall in at two degrees right and down, then you can shim the engine mount if you find you need more later.

2 degrees down and 2 degrees right, makes a good starting point. But, like anything else it may need to be adjusted/trimmed later.
Unless, of course you have a "flying" stabilizer, like the Telemaster.

OMG E.J.! You're using your Frankenstein Nexstar for your avatar? You are brave!