The 68-72 New process transmission Will Not Fit that bellhousing without some work. The New Process transmission is indexed at 5.125 inches. The bellhousing is indexed at 4.686 inches. The bellhousing will likely have to be bored out so the newer transmission will fit.
I ended up making an adapter plate for my 1940 GMC to put a NV4500 5 speed out of a dodge 1 ton. I used the stock bellhousing. I haven't dot it on the road yet, so I can't tell you how it works.
