ok im buying a th350 or th375 9in shaft,im told i can re use the d shaft,but what abt the trans mount?

 

YOu can use the mount.

That's the easy part though; the crossmember has to be changed. But, get the right one of those, and you can re-use your old mount.

 

if i tap new holes can i use the same crossmember?

 

No.

It's about 5 - 6" off from where it needs to be, and therefore the wrong length.

You need the right crossmember. No way around it.

No tapping involved. The car already has the holes to bolt it up.

 

Since you'll also need some way to attach the torque arm, it's better to just buy an aftermarket torque arm with a TH350 crossmember. The aftermarket torque arm will attach to the crossmember like it should, not like the way GM mounted it on the back of the transmission.