First, you have to figure out what your time is worth. Then, decide EXACTLY what he expects you to do. As said before there will be lots of time eaten up on this project in the way of "Oh by the way", and "While we're at it" jobs. Also, get in writing who is expected to furnish fluids, filters, cleaners, paints, parts, etc.. Nothing like fronting the guy the supplies and then having him try to stiff you.

Make sure the donor motor/trans are in good working order BEFORE you pull them. His idea of good running and your idea may be way different, and if it runs like crap when done it WILL be your fault in his eyes.

Is the donor wagon a similar year B body too or is it a C body? Add in all the things that won't work in the B body if it is.

Even at a cheap price like $30/hr, I can see this running up to $5000 easy enough if he wants you to supply all the parts.