What is involved in making this?

[cropwell]

The main thing about the neck plate is the accuracy of the bolt holes, the outline does not have to be super accurate. So you could put the guitar on a piece of paper and mark the hole positions, the outline could be just a guess based on the pic you provide (which is easily found on t'interweb).

However is it form or function you seek, because the function of the neck plate is to stop the bolts (or screws) tearing through and repair washers (penny washers) would do that job until you found that hen's tooth of a pre Mk4 plate. But it certainly wouldn't look pretty