Re: 80cc 1940 ZENITH with MONARK FORKS...
my first build was a 1947 Monark. At around 100 miles, though, the weld at the head-set to down tube just gave up from the vibration and detatched while I was riding it. It could have been a big crash, but the drive chain to the motor kept the thing from taco-ing till I could stop...the lesson; old, steel-tubed, frames with butt welded or brazed joints cannot stand the vibration for too long, they were never intended to be motorized. I'm not trying to rain on your parade, just letting you know what I experienced. Had ANY of the other welds been compromised, it would have been a nasty, uncontrollable crash. Since then I have built a Felt (check out "my finished felt 1903"), the welds are super beefy. The Nirves and Electras are also extremely well fabricated frames, and all your other parts could easily be transfered over.....good luck.