Morning Welsh... I got that feeling it ain't gonna be so easy. The bike doesn't even have a chassis number, but I reckon it might get one soon 😉 Decided to put it through its Manx day time reg to legitimise it a little bit, at least I'll have an export document showing previous road registration! Trawling Ebay for E stamped lights etc, I'm sure it's easier getting the stuff here than in SA.
Chassis number a definite, "E" stamp much less an issue and the testing stations are NOTHING like the UK (technical knowledge minimal), but the licence authorities like paperwork, proof of ownership, Police Clearance etc.
Speedo needed but a bicycle type one is fine, sidecars are almost ignored by legislation here, but getting a home built trailer registered is near impossible.

I know your island a little, my cousin raced there, back in the mid 60's my cousin was monkey and mechanic on the midlands sidecar championship winning outfit, they ran 750 Puma Triumph's then Konig boat engine two strokes, then TZ700's from memory. He still rides at 70+ probably much better than me.
The sidecar guys on here like Gerrard are quite well educated legally, they went into dodgy legal professions and will hopefully advise on whether or not you need to bolt in a plastic garden chair for the passenger to get it through the test.