The units were usually connected in such a way that they shared lube with the tranny. All the gears churning would heat that up too, so you should be fine. When locked out of Od there is only two bearings turning. When in OD the planetary gears are moving around their shafts and inside the drum. Just that little bit of oil should be fine. You could easily rig a convection circulating external tank. Drill a hole in your front cover right above the high fluid mark with the trans cold, and another around the 1/4 full mark. Connect hoses to a small tank... I think it should be at the same level as the unit. As the fluid heats up it would run into the reservoir and cooler oil would be drawn in from the lower tube. But I don't think it's necessary.
Just be careful cutting out of OD! As fas as I know the unit should be fine running in OD all the time, just don't pop the clutch and do any burn outs with it unless locked out! I'd also cut OD off if pulling a heavy load, at least for takeoff. If you run across another unit you might want to pick it up, even if it's from a different make. The planetary set should be the same, as well as the output shaft (though the splines could be different, I don't think so -- should be the same as Borg Warner T-10 output/yoke, also used on large three speeds and the bigger BW auto trannys). The input splines will be different though. If it goes the planetary set and output shaft (drum is made onto the shaft) will be trashed.