can someone please explain what this "rollover" noise is in FG's?? what is it? and can it be fixed? and does it effect the car at all??

rollover noise is cause by excessive clearance in the gear meshing teeth and the gear teeth chatters between both sides of the tooth and causes the noise. To reduce this noise they put in a sissier gear in there and this gear has more teeth than the driven gear there for it spins at a higher speed this gear is attached normally to the front of the lay shaft or cluster gear and it creates a load on to the teeth so that they contact mainly on one tooth surface instead of chattering between both sides of the tooth which eliminates the rollover noise .

A lot of FG manuals do it, and so do a lot of manual cars in general. It is to do with the tolerances in the gearbox (quite high in the TR6060), and the clutch. I thicker fluid will help NRO, but reduce shift quality, while a thinner oil will make NRO worse, but improve shift quality... it is up to you. If you are worried about the 1-2 shift being a bit notchy, bleed the master cylinder or have it bled by a pro.