As grumpy says, can we start by posting the essential numbers from the engine? These Model, Type and Code numbers can be found on the top of the valve cover, on early Intek OHV engines. Or on a plate on top of the cowling, for later ones.
Most of our Greenfield maintenance threads here on ODK are found in the
Ride On Mowers & Tractors section.
There is also our
'reference thread' on stripping and rebuilding a Greenfield drive. The pics there will be useful to you.
Grumpy, Greenfield has long used 'set screw mounted' clutch shaft outer bearings. The inner race is extended to form a collar, which has grub screws through it to lock it to the shaft. I think those are the 'tiny grub screws' in question. They are shown in the thread I've linked above.
Iceman, a good penetrating fluid and more heat are the next things to try on that sprocket. As the pics in the above thread show, the shaft is parallel, so it's just rust-bound, not locked on a taper.
If there is room to use it, a 'bearing separator' type puller is well worth a try.
As far as lights go, 12V LED reversing lights are available, and will be much easier to mount than conventional reflector lamps.
