There is no other written work on Trusty- that’s why I wrote the book!
The best thing to do is to buy a JAP 5 book off a well-known auction site; the original, official book has set-up instructions for the carburettor and magneto as well as a full parts listing and dismantling/rebuild instructions for the engine. Otherwise, if you need more help with the Trusty bit you can look out for the Trusty Tractor Parts List which does surface from time to time on the same site and , of course, you can search through postings on this forum for information on how to do various things. It’s been going long enough that there should be something about everything to do on a Trusty.
Once you’ve got it going you could do with a few tips from the Trusty Operator’s Manual; this you can get as a reprint from (I think) Japonica Press.
Engine parts for your JAP 5 should be easy to get hold of. Try Meetens Industrial Engines as a first port of call. One thing that I do whenever I can is to buy old and redundant engines at farm sales so that I have a stock to keep my fleet running.
Parts for the Trusty bit are generally not available. Bearings and bushes can be bought from your local bearing supplier, Whitworth and BSF bolts can still be bought from most suppliers, but apart from that you have to make or repair anything else. That’s what makes it a challenge!
Best of luck with it, and don’t forget that we will help whenever we can.