I was wondering if the 700r4 thats on my 3.1 will mount up to a 3.8l?

no it wont bell housing patters are different

how would you fix this?

If you use a 3.8 engine from either an 80's or newer front wheel drive car or a 95 or newer F-car, the tranny will bolt up. It's only the rear wheel drive engines from the 80's and older that use the Buick/Olds/Pontiac bellhousing pattern.

If you have an older 3.8 with the B-O-P bellhousing and you are trying to hook up to your 2.8 metric bellhousing, you should give that up. The best way to fix that is to get another transmission. You can either use a V8 700R4 and then put your F-car tailshaft on it (to hook to your torque arm) or you can use a 2004R transmission with a B-O-P bellhousing and then customize your torque arm hookup to your crossmember. Save yourself some headaches and buy a SPOHN crossmember to adapt it; don't do any homer welding jobs on it.

Good luck!!

it would be from a fourth gen firebird!