I'd go with a three piece conversion- much lighter weight- Sick Bikes has the wider axle , or at least I got a wider one there a couple years back- don't know if it's wide ebnough for the pull start though - I could sell you mine- I didn't really need it- I'll measure it.
Total length 135mm or about 5 3/8 inches
I see they have a longer spindle that's about $16 shipped -a 158mm-, and they have a cartridge complete long unit for
153mm "for pull start applications" $ before shipping18
205mm $25 before shipping.
and a 36 3 piece pedal sprocket may be a little hard to find , but not that unusual for an older road crank otherwise- a bit of a granny gear
some people use 20" bike cranks that are shorter