Haven't done any enduros myself,
only motocross and supermoto, wouldn't mind having a crack at it
The TBEC is Trail bike enduro club I think, they are trying to encourage the cheaper end of things with trailies etc, if you try a few others you may have more luck, usually converted motocrossers are more the preserve of the expert riders on account of sharper power delivery and so on, motocrossers usually have closer ratio internal gears, whereas enduro have quite a low first gear to cope with tight woodland and other technical sections (not quite as extreme as trials sections, but you may have to get over the odd log and big rock etc.) and also a higher top gear to cope with higher speed on fire roads and across moorland or even on the road between sections and stages. Enduro bikes are usually slightly softer engine set up, more torquey low down and in the mid range where motocrossers need sharper quicker snappier power to accelerate quicker up to and over jumps out of corners and so on. Suspension is also a bit plusher to soak up lower speed obstacles where moto needs ability to cope with big landings.
Anyway, as I say, try a few other clubs, also consider hare and hounds events and GNCC type events (Fast Eddy series) you have a few options, it's a case of it being slightly more difficult using a crosser, but it's by no means impossible! don't be put off!
as said above some things can be done to make road legal if that's neccessary, also the bike can be modded in some ways to make it more suitable, different exhaust, weight added to magneto flywheel, change of sprockets, different throttle twistgrip (slower action, to to open more progressively) revalved and/or resprung suspension.
Hope this helps, one of the best dealers to talk to or email about it is ET James in mid Wales, the heart of enduro country! they are at Rhayader, and Suzuki dealers for a long time.
Trials and motocross news and trail bike magazine are some of the best sources of info too.
Good luck, have fun, any more questions and I'll do my best, even if I got to ask someone else!!