Do you have a spare car to drive when the 40 is a week offline for maintenance?
Because I think whatever you buy it will need work, and some is a weekend and some a few weeks.
I bought at the lowest of the market so a lot of work but for me it is fun to buy new parts and spend a few grand (now finishing up the welding so it can go for the return road check)
What I found is most expensive is set of tires (but almost no time needed to mount that), full exhaust (but find the right one) and all brakes around is a lot of work to press new lines and fit it all with new brake shoes, drums, cilinders.
Suspension springs is very expensive (and time to slam it loose) but the shackles are cheap.
If you need to replace the rear iron struts, those are riveted with about 20 rivets: a hell of a job to replace (grinder or blowtorch or plasma cutter)
A good indication is the parts websites and scroll trough the available parts, all parts have their place, price, time, swearwords and blood.
But the hardest is a personal time limit on buying, many will follow so just drive a few and see and hear the difference (sloppy, bouncy, grinding, pulling to one side)