30mm sounds ok if standard spacers, 220ml should stop them topping out.
http://www.ebay.co.uk/itm/Fork-Springs-Trials-Motocross-Bultaco-Montesa-Pre-65-/220870238985?pt=UK_Motorcycle_Parts&hash=item336ce46309#ht_500wt_969
Fitted Boyer many years ago,(to a B40) no battery needed, everything came with the kit. Easy to fit, time etc.
Electrex also do a kit thats supposed to be good, as is PVL.
Think they are the same Marzocchi forks as the SWM, if so :-
2 seals per leg
approx 50mm spacer above springs.
I use 220ml tqf per leg. (But Woody recommends 200 & he's usually right)
If when putting the fork caps on you dont have to compress the spring by approx 30mm the springs may be past their best, I got a pair of 35mm springs from Bultaco for approx £27 delivered.
Anybody used this company ? (dont think Martin M does pistons)
Any other alternatives ?
http://www.ebay.co.uk/itm/SWM-and-ROTAX-280-O-S-Piston-kit-brand-new-76-mm-std-/140616769794?pt=UK_Motorcycle_Parts&hash=item20bd69a102#ht_500wt_1202
Thanks
Ross