There was an Engine Masters article where Buck Hinkle took an old 361 B and put a B based 3.74 crank offset ground from a 3.375" stroke B with a long 2.00" (327) SB Chevy rod and +.060 400 SBC 4.185" piston in it, so at the extreme with an RB 3.75" crank it looks like you could go easily to 4+ inches by going less than the 2.200 BBC journal, provided you can find a long enough and wide enough rod to work and a piston/pin combination as well.

Whether it's practical do do is another matter, buck actually also took the MAINS down to 2.45" SBC size and make steel bearing cap spacers to cut down on the bearing speed.