I have just put a 327 cid, came out of a 63 corvette, into a 73 GMC Sierra Grande. The transmission I have to use (because of money)is a TH350. I have an NP203 that I have no clue what it came out of. The truck was made for 4x4 but the output spline from the transmission is too long for the NP203 to bolt up properly. I need a square adapter for the 4 9/16 bolts that hold the Transfer case and Transmission together. My question is, where can I find one or can I make one?

I'm really good with engineering but I don't want to take a chance unless it's OK. I know the transmission being mounted to the motor is good enough to keep those two up. I know that the T-case mounted to the cross member and then pulled to the tranmission by the four bolts is enough to hold the t-case up but I need to make sure that the engineered adapter will not be effected by the excess weight of the transmission or by the power when in D or R.