Should the rear mudguard fitted to a OSSA TR77 be full length, as in down to the swinging arm or the shorter type. I am thinking the Gonelli type mudguards.

Now to the middle exhaust box, should this be packed/repacked with exhaust wool or is it an empty expansion box with a baffle tube inside?

The TR77 with the black frame had a full length mudguard in that funny off-white material. The later TR77 Verde with the green mudguards also had a full length guard but they weren't the Gonelli Bultaco type.

Now, the Gonelli is the only option for a green rear guard but fitting one without some sort of lower section will leave the back of the engine exposed to all the crud off the back wheel

The middle exhaust box is a perforated tube and packed yes.

I've never been into one of the TR77 type rear silencers but I've been told by those that have that they were packed with wire wool and have the two exit holes at the rear but underneath, not out of the end. Apparently, the mod was to rip out all of the wire wool, weld up the holes and put an exit hole out the rear as normal - but I've no experience of that so can't comment.

What I did on my two MAR models was to make my own end silencers by using motocross / enduro back boxes, about 12" or so long, with the innards replaced with a trials size perforated tube (25mm in my case and straight, no bend) packed with wool. Keeps them quiet and the 310 in particular revs like hell.

Thank you Woody, my bike is a Verde model but until the frame goes off for powder coating I am unsure as to the final colour? Normally I like to stay true to the original colour but the all over Kermit look is a bit of an eyeful.

The back box is an add on or aftermarket alloy straight through type, 24mm dia inner perforated tube and wool packed, middle box appears to have no packing at the moment and a rattley baffle tube so it needs some attention there.