If you used this type of set up the gear reduction would be like a clock.
The threaded rod raising the grill lets say had an 8 thread per inch pitch or lead.
Every turn would raise it 1/8th of an inch.
Then add the worm drive depending on what ratio that was would really slow it down.
Too brain dead to figure it out but you could be looking at 100 turns of the wheel to get the grill to move an inch.
If I follow it correctly.
Everything I have came up with so far involves some sort of contraption.
My best idea is to use something like an OS&Y valve has to move the grill up and down.
I really do wish I would have scrounged more when I had the chance in the plants.
By darn I just figured it out and still use the overhead cable.
Worth