Re: Bottom crank jack shaft.
study the pictures in the link I posted
using a bmx freewheel will not work because its pedal start
the 2 sprockets on the freewheel SBP uses act as an idler until you pedal then it locks up
by putting a sprocket on the left side and running a chain forward to the crank with pedals keeps it simple and made with parts that are already made.... IE no custom parts=no machineshop bill
Live life as its your last day... it just may be
Learn to do it right or how to fix it later, quicker to do it right the first time.