To assist your efforts, I went through the Table of Contents and Appendix 1 of my book to remind me of items I had to fabricate or purchase (or might have had to purchase) when completely rebuilding my 1928 Model C.
https://www.amazon.com/Ariel-Chronicles ... B0BN61Z6H1
Also, I fabricated approximately 30 special tools and jigs, but below only have listed a half-dozen of the more general ones.
piston with gudgeon pin (Omega piston gives the right balance factor)
rings (these come with a new piston, but ideally also should be available separately as replacements)
small end bush reducer
valves
valve collets/keepers
valve guides
valve springs
pushrods
metric spherical roller main bearing with ID resized to Imperial
timing-side bush
oil pump
clutch plates
clutch springs
clutch bearing rollers
engine sprockets (19T, 21T, 23T) [note: several incompatible cush drives were used]
gearbox sprockets (19T, 22T)
variable magneto sprocket (made by someone in Australia)
gearbox bearings
brake linings
wheel cup/cone bearings
Special Tools
magneto sprocket extractor (stock)
magneto sprocket extractor (variable sprocket)
1¼ BS deep socket for gearbox sprocket
clutch hub sprag socket
socket for adjusting tension on clutch springs
brake pedal extractor