Acually cutting the input down has been done quite a bit, GM & Ford inputs only have about 1.25" bearing surface or their inputs, mopar has about 2" & a larger diameter for more surface area...
But on the flip side, if you have access to a mag drill or can rent one the crank could be drilled with the crank in the engine & the engine in the car, you would likely need the replace the pilot bushing as it would act as a guide for the drill & be damaged, but it is doable..