UPDATE...
Well, after a weeks of bashing, got round today to striping car down, quick clean and prep ready for the new F3.5 Pro & 17T bell. Strip down went well, no rounded screws or hex bolts.
Couple of things I did notice, the F3.5 or taller than the F3.5 Pro. This is in the cooling head though. The carb sits a lot prouder on the F3.5 Pro and required the throttle linkage to be relocated to the top of the servo arm and it extended a touch. Other than that, everything was straight swap.
One potential issue may be the 17T bell and it's mesh with the pinion wheel. It's tighter than I would like, but I can't space the engine out any further. I will keep an eye on this, and if needed, replace the pinion wheel for a slightly smaller one (more top end again).
All ready to roll for tomorrow's running In....
Stripped ready for cleaning
F3.5 Pro Fitted and Car Cleaned
New Engine Heater
Shell Fitted