I'm not Chris but yes you can do that in the car by pulling the valve body. You can also check the front band servo and servo bore with the trans in the car. You'll need to back off the band adjustment and remove the band strut.
Hey Hey, Jones or Chris, might this ALSO be my problem with my 904 not wanting to upshift into drive until 40-45 mph? I have that restrictor plug in mine because it came with the TCI kit and said to put it there. I have posted regarding my trans not wanting to upshift to drive. Any help would be GREATLY apreciated.