WoW that is amazing, I wish I could find a load like that!
Really, if you find your not up to using the batteries or finish your project and don't use them be sure to pass them around, there are a lot of EV'rs who would like to play
I would say follow the KISS principle and the KICS principle (keep it cheap)
Whatever you have access to including that little golfcart would work as parts and the motor in the golf cart would definately be big enough to drive a motorcycle or trailbike, maybe not super fast but keep the weight down and it would work as in town transport and if it is a larger golfcart motor AKA 5hp or larger you can probably modify it to get up to 55mph on a light vehicle like a motorcycle or even a small aerodynamic car (like my subaru 360), occasionally junkyards have vehicles that are OK but have a blown motor most are getting quite expensive even though the price of metals has dropped.
Go to diyelectriccar.com and bring the model of motor in your golfcart you might be surprized, both of my ev's use golfcart/forklift motors and one does hit 55mph at 72v, though it is a 10hp which are not as common. You may need to tune your motor a bit differently, advance/replace brushes, to get it up to speed but don't underestimate as long as the vehicle is light it should be enough assuming it isn't a little 2hp plug
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As for donor vehicles generally look around classifieds for motorcycles and cars that do not run or place an ad on craigslist (stating what you are attempting), if your area is large enough you might get lucky and find something suitable.
The best EV is the one that is the most reliable, that you don't invest money into but you do invest time and ingeniuty into.
Good Luck
Ryan