rb tunnel ram on a b motor

hi all,
i'm struggling to find a tunnel ram for my 383 for reasonable money here in the uk. i've got a lead on one for a 440 so if i get it the plan is to narrow the base (cut a section out of the middle, lengthways), weld it back together then adapt the top back on. the ally welding isn't an issue, but any other problems i may not have thought of?
cheers, neil.