I have a 396 TH400 in a 55 Cameo. Is the small block front mount located on the front crossmember, or on the sides? If they are on the front, it is easy to fabricate two L shaped brackets that will use the original mounts. The older bellhousing with the rear engine mounts work great with a standard tranny. The only hassle, is that you will have to bang the firewall back on the LH side to clear the cylinder head. I used headers because the LH exhaust manifold will not clear the steering box. I installed the 396 in 1971, and have never regretted it. I am replacing it with a 454 because I have a fear of my head hitting the steering wheel when I leave an intersection.
Bob