Elsewhere in this thread. Anyway, here is what I had said:

There are “electric truck” conversion books from the 1970s. (Only trucks as they used lead acid batteries, which are still extremely heavy for useful amounts of stored energy.) This indicates it is not extremely complex, though possibly still very complex. (My reason for this assessment is from reading a few of them, but never implementing any of it.)

Anyway, here is a title to look for, from 2011, " The electric vehicle conversion handbook : how to convert cars, trucks, motorcycles, and bicycles : includes EV components, kits, and project vehicles" by Warner, Mark, ISBN: 9781557885685 1557885680.

2021's "Convert It!: A simple step-by-step guide for converting any classic car into an electric vehicle." by Ron Toms, ASIN B093CH8HR7.

Neither are from the 1970s, but both are likely more useful anyway. There are also likely others that I cannot immediately find. I have read neither, yet.