90 degree old style cranks , that just barely clear the chain-stays are the lowest practical Q ..

I think you are in the realm of Quantum mechanics .. unless you start from scratch.

back in the past Hanebrink made a really big ATV tire bike the crank turned a jack shaft, the jack shaft
in turn turned a cog much further outboard to clear the tire..

so the primary drive was as narrow as you wish.. But even He is not making the ones he does now like that ..

so you are in the hire something Custom , realm if it matters enough , what it costs wont ..

if you are not aware of how these things can sort out.. other than just a regular bike.

back in the 60s a friend's dad made a Jack Shaft bike drivetrain..
there was a 3 speed hub up in the upper seat stay with a second cog on the hubshell.
one chain went from the crank up to the cog on the hub driver..

then a second chain went to the hub in the wheel, driven by the cog on the hubshell..

so it was a 6 speed ... 3 speeds in each Hub.