Electric Motorcycle motor and controller?

I have extra components from multiple motorcycles, enough to make an electric bike. I just need the motor and controller. I have a source for 12v SLA batteries sold by the pound, and a wide array of fabrication tools. The same source (a closeout and refused freight liquidator) has a wide array of electric motors,... show more I have extra components from multiple motorcycles, enough to make an electric bike. I just need the motor and controller. I have a source for 12v SLA batteries sold by the pound, and a wide array of fabrication tools. The same source (a closeout and refused freight liquidator) has a wide array of electric motors, but I don't know what I'm looking for.

They are WAY cheaper than any retail/online option, but almost nothing is in retail packaging, or even industrial packaging. Usually it's just the item with whatever factory markings are on it. So I need to really understand what I'm looking for on a DC motor that can power a large-ish motorcycle. (85 Honda Shadow VT700C frame, seat, wheels, etc. The engine has been removed, as have the electricals, airbox, etc. It's bigger than a Rebel, which is a more common base for an electric, but it will also accommodate much larger batteries and rider.)

Also, what am I looking for in the way of a controller? Pointing me to an online DC controller primer would be sufficient here. I learn very quickly, but I'm tired of my online searches leading to sites selling complete kits. I want to design my own, because that's how I do things.

I know plenty about SLA batteries, including wiring and charging. But my use for them in the past has not included DC motors and/or any sort of throttle setup. My experience with potentiometers is limited to the audio systems I've designed in the past.

Oh, and I'd also like to know the best (or, rather, most economical) way to convert the power back down to 12v for the headlight, turn signals, and possible sound system if I have enough power to accommodate the weight.

I'm unemployed and I'm rebuilding old bikes for cash. This is just a side project that could potentially also earn me some money. So I need the best bang for my few bucks.

Thanks!
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