That part of it is okay, as the manual I have shows that both the FC and EJ use a Lucas RB310 regulator, although you have to tweak the settings a bit.

I bought a reco generator off ebay a while back as the guy said it came off his EJ, I stored it away till mine started playing up.

I went to do a changeover yesterday but it doesn't fit, I have a couple of manuals one which covers all models up to EH, it appears I have been sold a Lucas C39 which is from an FE whilst the EJ takes a C40. The C40 is a bigger generator which is why it doesn't fit, I also have another C39 in my shed so I was wondering what I have to do to get them to fit properly, I'm guessing all the difference is that the FE grey motor had a different mounting bracket, am I correct on this?