Thanks for the input guys!
I'm in the UK. I'll make sure I plan for plenty of time for the rear end and I'll look at the steering rack issue. This is a long term project, so I'm not in a hurry.
Sorry, I wasn't suggesting that I thought I could use the donor's tank. The pump and sender assembly both sit in the tank, so the two options in the Haynes manual wouldn't work.
Any ideas where I can pick up an MX5-ready tank?
I'm thinking of using Phil's TMXR chassis and wishbones because I'm not confident enough in my welding skills and I don't have any friends who are.
J