Thanks for posting. Yes, judging from the shape of the gear arm this looks like the 39-188. We have come across this situation before, where the old link arm is a different length. There are a couple of solutions you can try. First, you could try installing the operator as is--there's a chance it may work just fine. In the event that it doesn't, you could try and adjust the bracket on the sash to which the old 4-1/2" long arm is attached so that it will better work with the new 5" long arm. A fallback solution is to drill out both arms, then put the old 4-1/2" arm on the new operator using our 62-014 rivet. Let us know if you have further questions about any of this.
