TwitchTrials

No worries. Ah yeah, of course! I must have filed off that lip when I did it, or, just smashed it on with a mallet knowing my way of doing things back then... ...however, you could just make it 6 speed and continue with everything else already mentioned. I'm not sure the high limit screw will reach all the way to 6th though; you might have to move some spacers about until you get it where it needs to be. First port of call, for me, would be to loosen the cable and wind in that screw, see what gear it rests in/near and then decide on where to go from that.

Hey, Well, after snapping my chain nearly 6 years ago I've since not been on a trials bike until a few weeks ago when I decided to rectify the chain issue! That and I lost all my old account details so new chain and new account... hopefully some more riding too.

Yeah you can, you'd need spacers on the hub though and, although I guess not totally necessary; see if the high limit stop screw can hold the derailleur at the 7th-ish gear. I'd personally run the cassette the closest inboard I can with the bulk of spacers on the lockring side. Adjust your high limit screw so it runs smoothly on the highest gear/smallest cog with no cable tension. Make sure the shifter is in the highest gear available and tighten the cable, this ensures you wouldn't have loose cable as it would only shift back down to the 4th position in the shifter, and the low limit screw would prevent any further up-shifting. (whereas if you did it the reverse there's nothing stopping you shifting into 8/9/10 once the derailleur has hit the limit) B-screw will likely need some adjustment as well. If that way doesnt provide smooth shifting then I'd do everything the same but with the cassette spacers all inboard.