I recommend you go to Riverside Flight Centre for the FAA IR. Then go to Airways Flight Training in Exeter to convert. They use the same checklists and BE76 (Beech Duchess)aircraft fitted out exactly the same way- you'll end up very well prepared for the JAA IRT.
FWIW, I went to Riverside and ended up doing a CPL/IR (ME) and then converted the IR with BCFT in Bournemouth, who were also very good. Given the benefit of hindsight I would have done the CPL with Oxford Aviation Training in Phoenix.
Any more info, give me a ring (I've PM'd you my number). I won't be checking my email for about until about 20th October now, so this is the easiest way. The route you're taking is almost exactly the same route as I've taken.