Sounds like what you need is a bottem PTO! They replace the bottem plate of the transfer box and provide an extra rear PTO, so you could leave the OD in the normal PTO place and run the rear mounted gear off the lower ones.
They were most commonly used on vehicles needing to drive kit underneath the middle of the vehicle, or ones with a front mounted drum winch aswell as rear PTO as unlike the fariey capstan winches, drum winches were hydrolic or shaft driven from the gearbox (shaft runs between the chassis rail and the engine on the left hand side).
Down sides, they reduice ground clearance, and perhaps because of that, and the fact few people needed them, means they are pritty rare. If your lucky enough to find one you could give it a go, but I think your best bet is to ditch the overdrive - if your planning on using it as a local hack at speeds under 40mph you won't really need one. Doing 50 without an OD is only really uncomfortable in a diesel for sustained pereods.