Replacing a rear window motor/regulator on a Spyder convertible.

My son and I do weekend work on his spyder convertible and are to the point of repairing his left rear window motor. We have a new Denso motor/regulator (we suspect it's a right not a left tho- arm casting clearly has an r stamped on it). We're past removal of the side panels, speaker and speaker holder and puzzled at how to access the window unit itself. Appears to be inside a welded side panel with a small access hole too small to allow access/removal of the window and regulator. Do we come at this by removing the rear left quarter panel? If it turns out the regulator is for the right and not the left can we swap the motor out instead? We won't be getting back to it for a few days but sure would appreciate any help.