Me mate fitted one to a Citroen 2CV8, a rover V8 powered 2cv on a stretched MG BGT chassis.
He used a corsa b motor, you can run direct to power for 100% assistance all the time or use a p/s ecu that came with them so it varies according to speed, or the other way is to get a potentiometer from ebay so you can set assistance how you want/set amount.
Having space would be the biggest issue, but also look at rover lecky ps often a lot cheaper and more compact as well.
tabetha