I recently acquired a pair of these for use on an eventual project.
Retro-fit kit to manual window | RSR 911 - Robert Sikkens Racing
These converters replace the electric window motors and allow you to fit a manual crank.
Description from the site...
"This kit enables you to use the original electrical mechanism of the power windows, by removing the electric motor and replacing it with this item.
The installation is quick and easy, just fix the pinion of our kit as close as possible to the ring of the original mechanism, making sure not to tighten them together too close.
modelli: 911 ’74-’89, 964"
I haven't installed /!tested them as of yet, but they look & feel brilliant. I wish I'd known about them before installing manual Speedster window regulators in my current build (they required modification/ reworking).
The converters weigh 3.85 ozs each. The electric motors they replace weigh 26.24 ozs each, which equates to a ~2.8 lb weight savings.
Shoutout to @anil999 for sharing these convertors on this thread:
Going full manual (windows, locks and mirrors) 1989 doors. Tips & tricks?