""OR a new set of cotter pins.
Which do you think is the easiest to accomplish?""

Obviously if you can find cotter pins then that sounds easiest. It all depends on if you want it to look original/classic or you simply want good performance. If it were me, I'd go for both.......you can a nice, used Campagnolo Nuovo Record Crankset and Nuovo Record or Victory 68 X 115.5mm BB on eBay for $100. That suff looks classic, is lighter-weight, performs well and maintains value.

If you just want good performance...get a used Shimano 600 crankset and square-taper Shimano BB for $50

Otherwise, keep it totally original and get cotter pins.