Here are the pictures and information on the struts used on my 3700RL. When fully extended, the strut is overall 21" and the sockets which connect to the bracket plate studs are at 20". The following information is on the label attached to the strut.
IGS - International Gas Spring
Volumeline
Romeoville, IL 60446
(815) 553-0253
8RU203468BB0089 10/11
20 lbs. Force
The lower brackets are the same as the brackets on all the other door struts. They are mounted right above where the curve of the door radius corner begins.
The upper bracket is also the same one used on all the other doors. These have not tended to loosen up as the others on the bigger doors have done. I suspect it is because the 20 lbs. struts don't exert enough force for this size of bracket.
The top edge of the top bracket is 4" from the door edge. The lower bracket is located as far down as possible. Since your doors are around 4" shorter than mine, you should measure carefully to ensure the strut will fit and operate properly. Maybe an 18" strut would be a better fit.
If you need anything more, you know where to find me. If you want full size pictures, I will send them via email.