Mile Marker hydraulic winch issues

Hello people, i brought a milemarker H12 winch from ebay to fit to my 1989 land rover running a 300tdi, it was removed from a 200 so the belt and pulley were different so i contacted first four and they supplied me with them. but i couldnt justify there £58 for a new mount so modded mine to fit the timing case but the belt is too short when the idler pulley is fitted and too long without it ?
has anybody any experiance with this type of winch pics would be great if possible im pretty confused.





thanks Sam

measure with piece of string or beller still nylon flat parcel band- add 15mm and then see if friendly local motor factors can supply a belt- that's what I did for my conversion.

secondly is the pullel smooth or toothed