Iain - Whopity basically said it all - just give them a ring at Turweston and they will advise, they are usually very helpful. BTW, so as not to confuse NPPL HQ when you ring, the NPPL categories are SSEA and SLMG - you'll get extra brownie points for the correct terminology
I fly a PA28, but I have flown Grob 109Bs on a number of occasions - in the air I thought it was a very pleasant aircraft to fly with good visibility, nice handling and I much preferred a stick to a yoke - far more intuitive. On the ground it takes a little getting used to after a trike, but you'll find that it all slots into place after a few sessions.
The stick+throttle / airbrakes+stick changeover always seems a bit clumsy to me and ideally I'd like to see a single airbrake lever in the centre, but I suppose that's the gliding heritage making its presence felt.
Good luck with your training - have fun!