First of all, I'm by no way a purist. I helped my brother sling a EFI 350/700R4 into his 1960 F100. I'm also getting ready to put an EFI 383/700R4/NP241 in our Scout 800B (you want to talk about purists freaks, try posting about this on binderbulletin.org and they bite your head off). That said, in this case I would have to aks why though? I suppose if you already have a complete drivetrain lined up (350/700R4/NP241) and its all you can afford, then go for it! But, to otherwise adapt the mounts and get adaptors, its just not worth it. Plus, in the case of the F100 and the Scout, both came with outdated drivetrains in my mind (292 and 304 with 3-spd trannies) compared to what could be cheaply swapped in and what we stood to gain (EFI, 4-spd overdrive, 2.71 T-case, etc.). But with a Bronco the mounts are all there for a drivetrain that is 100% still relevant and equal or superior to what GM offers.
Either way-good luck and post pics for us pic whores ;D