No, no inspection plate, or extra space on the shifter. I think creating a return port would mean drilling the transmission casting. Doing that competently is beyond what I can do. I don't see an alternative to returning at the dipstick hole, and I have no idea how to provide a dipstick after that.
If you decide to do it which may not be necessary if it worked before satisfactorily 10 years.
Nipple, a tee,plumbing in to the tee, a pipe plug on top of tee and that is what gets drilled and a dipstick added to that. The fluid level should be correct if its right before you do the new valve or compensate as necessary. Obviously the pipe plug would have to seal and a wrench used every time to check it not as handy as before but workable. my .002