I am in the process of swapping out a small block with T350 trans to a big block and T400 in my 66 Chevelle. I'm having a real nightmare with the trans crossmember. DO I need to drill new mounting holes??? I assumed the crossmember would go back to its original position. Obviously incorrect. Any assistance is greatly appreciated. Thanks!

Yes, you will have to drill new holes in the frame for your crossmember, because the th400 is longer than your th350. BB or SB doesn't matter. You will also need to shorten your driveshaft.

Bill

That's what I figured but certainly appreciate your tips. Thanks again. Mike