simplicity Shaft and Pulley Help

[mn8n]

Well I have an older simplicity two wheel tractor. Old engine was blown so I threw on one of those HF cheapo 212cc motors (works good for cutting with sickle twice a year) but now I am having pulley and shaft problems for the wheel drive. Does anyone know what the diameter of the wheel transmission pulley should be? The past owner had on a 3/4" shaft pulley shaft measures 5/8" but they used a spacer to make up for oversize) with a 8" dia. pulley.

Also, the shaft seems to pull out from the main housing and I was wondering if this was normal or how do I know where the correct position is?

Thanks for any help.