Thank you.
Having done some more research on this I have drawn the following conclusions:
1. Modifying will immediately lessen the market value of my amp (JCM800 2204 Master Model 50W Mk2. Lead). Not that I want to sell it...yet!
2. It
would be nice to put delay/chorus/reverb etc. in an effects loop, but for most situations in
my musical world, it's not really important enough...I'd just use all the effects into the front for gigs, and for recording they'd all be added afterwards.
3. Instead of hacking my beautiful Marshall, I'd prefer to buy another head with a factory-installed effects loop and use an ABY box. Although I'll have to get another cab...and a bigger car as well...and a roady...errrr.....
I love doing electronics, but I've decided I'm going to steer clear of this mod and get a higher-paid job!
Thanks for the information though, I'll be keeping an eye on this site

Rob