Congrats, an excellent choice of rib
If you would like a copy of the owners manual then there is one on my website hosted by DJL, feel free to help yourself to a copy.
Have a chat with JBT, (Riva on here) and see if they still have some spare drives. I suspect that the easiest drive will be to put a Sternpowr 103 back on rather than mess about converting the transom.
If not they Lancing marine will have, although they are not cheap (nor are JBT)
There is also a company called Folly Ribs in Cornwall that may have a spare engine or drive.
There is one Pacific with a John Deere 110 hp in it. Del Connolley re-engined it back in 96 time and said that although it had less hp that a standard rib it was quicker, so may be worth looking around for an alternative if you don't wont smoke. Mermaid are also very helpful and always seem to have a workshop full of various engines being rebuilt, well worth a chat with them or even a visit if your down Poole way.
Oh and don't forget some photos of the rebuild.