Hobbsy,
I think you may be incorrect when you say that you would need two taper roller bearings on a crankshaft, - one for the front and one at the rear. - could the crankpin take the bending stress applied by the preload required?

Two taper roller bearings, (opposing each other at the front, and a simple needle roller at the rear, or in the case of a cantilever crank, two at the front only, would be good.
This however, is theory, - In practice, space required, weight and cost would also come into play for production models.

( You may feel free to disagree of course, - but please say why! )