tyre size equivelents/ST greenlaner

[FatAl]

I am considering converting my R80st to use for some gentle greenlaning, the standard tyre size is front: 100/90x19 and the rear is:120/90x18. Tyre choice seems a bit restricted and I dont particularly want to spend out on having the front wheel relaced to a 21"rim.
I think Pirelli MT60's may fit, but the rear tyre size they quote is 120/80x18 would that be ok? Can anyone comment on the performance of these tyres? Any suggestions for other tyres?or suitable size alternatives? Would conti TKC80's fit?
Iwas thinking of keeping the standard front mudguard, would it be too close fitting for off road tyres?

Also does anyone know if the engine bash plate off an R100/R80 GS, G/S will fit an R80st, or are any aftermarket ones available?
Would I be right in assuming that GS handlebars would be a straight swap?
Thanks chaps.

 

[Tarka]

I got the wheels rebuilt on my 1987 R80G/S to a 2.5 inch rim, and fitted a 130/80 tyre.

I`ve had MT50/60s on it,also T63 Michelin.

The only slight snag was when I got the Spax monoshock spring powder coated,and they loused it up,putting a very thick coating on it. This made the very outer knobblies rub on the edge of the spring slightly.

You should be fine,but check clearances,as I recently discovered there are a few different offsets used within a similar model assembly batch.

G/S bashplate should go on ok.