Allis B10 generator belt issues

so a few months ago I stumbled upon an Allis B10 with an engine swap that looks to have been painted flourescent orange at one time, then a hasty coat of black over top. It has lots of compression and runs- ran- before I removed the carb since it leaked...

Anyway, it has one of those 'multi link' belts that you can remove some links to create a shorter belt. The starter-gen cranks over, and it slips on the belt. It has an idler pulley on the bottom of the gen bracket, but was told that that is not supposed to be there.

So, I'm thinking that it's the belt, and the 'links' decrease surface area, causing slippage.

Any advice, or pics of a 'correct' setup?
Thanks,
Matt

P.S. Being that it has an 'older' (no crankcase ventilation port) air filter assembly, I'm looking for a unit that'll fit properly...