Don't mod it! Blackface fenders don't benefit from an fx loop and there are too many hacked bassmans around. They have a completely different preamp design than a tweed fender or modern fender. Less gainy! Much less...
Heres some thoughts:
If you are driving the amp at all with your dry signal, most of your distortion is coming from the phase inverter or power tubes so an fx loop really won't help you. I would play the amp bone clean at 3 or 4 and use my pedals OR i would ditch the reverb and just use some tasteful slapback for ambiance and let the amp generate my tone. Maybe a little tubescreamer or fuzz. Or you could bi-amp and dedicate your modern fender to ambiance. Get a DI box and put it between your bassman and speakers. Then take the line level feed out to your delayset 50% to fully wet and run that into the clean channel of your modern fender with the reverb cranked and the amp eq set to taste. You can dome cool things shaping your delay and verb this way. Its like a toned down wet/dry/wet rig... I used to do the w/d/w thing with a showman and plexi. Its a lotta hassle without roadies, but a loud dry amp and tamer wet amp can work well... Experiment.
Me? I eschew reverb live. Its usually lame. Delay sounds fine into light amp od with a tubescreamer or fuzz out front. I actually run my flashback x4 before a nova drive into an already crunchy hiwatt style amp. It sounds right to me. The delays are less pristine but they sound good being distorted a bit!
Effects loops are for high gain guys like satriani.
Don't you already have a multi amp rig for stage work?
EDIT: you comment that the amp is SO CLEAN. Whats the problem then? Run it all out front. Or are you concerned with switching multiple pedals? There are solutions for that. There's nothing in my rig right now that does not have MIDI implementation and preset capability though my dry signal is 100% analog, only the actual echoes from my delay pedal are digital, everything else including drive is MIDI controlled analog. You could drop some of your gear in favor of MIDI enabled stuff, get a MIDI footboard and get a small looper for any traditional boxes you can't do without. I see you have an SD1, that has a mediocre buffer, it might be better in a loop... I just picked up a MIDI controlled dual loop to incorporate fuzz and analog chorus into my rig. Its doable, you just need to be a smart shopper!
