Transmission cross member issue (Help!)

[tranz am]

I am about to convert my 69 gmc from the original 307 & 3 speed to a 350 & a 4 speed m21. I see that there is no cross member under the 3 speed and that it attaches to mounts at the bell housing. The unit I want to install doesnt have the provisions for this mount set up on the bell housing. I want to use the large bell housing that accommodates my 11 inch flywheel. will the stock bell housing accommodate the 11 inch fly and will the M21 work with it? Also can I find a cross member to use with my M21. Will one from a th350 work? Thanks