What's the issue with the stock cranks?

I wouldn't assume anything just on number of splines and spindle size. Even 48 spline cranks that are standardized on Profile brand can be wonky when swapping parts around.

Got curious and looked to see what the longest spindle Profile makes and it's way shorter than that. They are into making weird stuff though, if didn't mind paying I'm sure they could make a longer spindle.

If it's just standard English threaded it might be the same bottom bracket shell some of the fat/snow mountain bikes are using. A MTB fat bike crank might work, I think the shell width is 100mm instead of standard 68 or 73mm.