Standard Lawless drives with FE adapter use standard cable. Drives that have been machined to accept FE motor without adapter requires a shorter cable. I had mine made at 3 7/8”. Most applications would probably work fine at 3 3/4”. At 3 7/8” with some motors I still have to cut a little of of armature shaft for a close fit.
I can’t answer that one. I was speaking of the 3.5 drives. I did talk with Fred this past week. I think that there are little to no machined out 7.5 drives out there. But, since standard 3.5 cables work with the FE adapter. I would think that a standard 7.5 cable would work using an adapter. A quick call to him would give you the most correct answer.
A few answers to clear up any confusion.
I get my flexshafts from Hyperformance, including the special ones for the "low" style FE setup. The cables I have are exactly the same as the ones he sells on his website, with the exception of the short one which is special, and they are made to 3-3/4" length. They are longer than the Thunder Tiger flexshafts by about 1/4", and TT shafts are just a bit too short for the FE conversion. .
The 3.5 and 7.5 drives were designed to be very close to 100% compatible with the K&B products, with one exception. The teflon sleeve in the 3.5 drive is one gage smaller than K&B uses. The machines groove in the drive is properly sized for the smaller sleeve, so you can't use K&B sleeves in that drive.
The only difference in the 7.5/11/13 cc application is the mounting plate on the 7.5 size drive. The 11/13 size has a different pattern and they are thru-drilled, not tapped. Since Rossi motors have a raised ring around the output shaft, I also make special mounting plates for them.
I hope this helps.