Get the 76 motor, trans, crossmember and driveshaft. Leaving the 61 crossmember bolted in place, cut the center 1/3 out of it. With the motor and trans in place and positioned, cut the center 1/3 out of the 76 crossmember, bolt it to the TH400 and weld it to the outer thirds of the 61 crossmember.
I don't know if the motor mounts are different, but I would also get the stands out of the 76 while the gettin' is good. If need be, then you can bolt them into the 61 or alter them to what you need and weld them in for proper placement of the motor using the stock 76 rubber mounts.
Pay attention to the placement of the motor front to rear so you can utilize all the stock cooling system components from the 76. You may even want to snag the 76 radiator, shroud and core support so the whole thing will be an engineered package. It's no big deal to swap the cut-down 76 core support into the 61.
You might get lucky and the driveshaft will bolt up. If not, with weight on the tires so the suspension is loaded, stick the TH400 trans yoke onto its splines on the trans output shaft. Push it in as far as it will go, then pull it back out 3/4 of an inch. Now, measure from the centerline of the cross and bearings on the trans yoke to the centerline of the cross and bearings on the pinion yoke. That will be the dimension you will give to the shop that will make up your shaft. Take both driveshafts and your measurements to the shop doing the work. Expect to pay $150 to $200 for a completed, balanced shaft.
Last edited by techinspector1; 07-27-2008 at 01:57 AM.