Here's a 4 page thread outlining putting a 428 in a 57 Pontiac, your car is comparable to this swap:
http://forums.maxperformanceinc.com/...d.php?t=559390
The alternative method would be to fabricate custom mounts from the frame to the late model side mounts and install a rear crossmember to support the rear of the T 400. Speedway motors sells a rear crossmember kit that is a cut to fit your application.
Since there were no T400 applications when Hurst made those swap kits I really don't think you're going to find one especially for your application.
Bill Eveland in the thread I linked to has a 55 Chieftain gasser with a 455 in it, you might PM him to see if he has any suggestions on how to make the transition.