I think I have a rebuilt rvf shock, its got a nut welded to the top of it just beside the top mount and an Allen head bolt in it.

I was going to swap it out for the '89 vfr shock I have in my vfr as the rvf shock has a little more adjustment in it compared to the vfr shock and if the rvf one has had a rebuild it should be a better unit.

Is there any way I can test out the rvf one other than fitting it ?

It looks like the stock spring is on it too, is it worth putting a different spring on it to cope with my lardyness ?

As far as I know the rvf shock isn't rebuilable Rhory, I'm sure someone will be along soon to explain this further.

Ill put some pictures up later then to show the nut and Allen bolt to see if anyone recognises what's been done.

Sounds like its been re gassed at least if you have a nut welded ontop. The builder will normally drill the hole, insert a piece of rubber into the hole to make it airtight and then they can put a needle through with an airline attached to fill it back up with nitrogen to the correct PSI weld the nut on and screw the allen bolt in to secure it.

Unless they have done the oil too its not likely to make a massive improvement, if i get a chance ill dig out my spare RVF shock and see if there is an obvious way to change the oil too but i doubt its possible.