Are your cooler lines still going through the radiator? If so then the coolant should heat up the trans fluid enough to check it I would think, I would try to make it work with how you plan on using the coolers instead of bypassing them and then having to go through more changes once you hook up the coolers.
Yep still going through the radiator. I put a large aftermarket cooler in too that replaced the factory auxiliary cooler since I went to the larger lines. The last time I ran it for an extended amount of time the cooler lines were warm but didn't get very hot, witch I was happy about..
Not bypassing anything, just thought if I put a pig tail loop in the return it would keep the converter from draining down.