Can anyone tell me the part number or dimensions of the circled part?

Part #910 340 Adaptor ring. That is their spelling in the Lockwood catalog. It is usually spelled "adapter" I can't give you any dimensions tonight. Maybe tomorrow?

Thanks Greg.  I can't find this part anywhere so I'm planning on making some spacers and need to know how long they should be. And the bolts I believe are M6x70.

Bob, The adapter ring is approximately 2" thick, and 8" in diameter. If you need more exact measurements let me know, and I'll try to get you better numbers then "approximately". I would suggest you look for a used one. You might check with Steve Beatty at Air Screw Performance. There should be a lot of "derelict", and worn out 277 out there.

Thanks again, Greg.  I bought some spacers that seem to work, they're 1" long so I used 2 with a M6x75 bolt.  Once I get the engine running well, I'll mount it on the plane and prop start it.  I wanted to use the recoil starter on the test stand.  The starter engages the starting pulley mounted on the flywheel with the 2" spacers in place and I imagine the distance isn't critical so long as the rope doesn't come off the sheave.

Bob,

Call Jbird up in wisconsin, he has a few of these laying around for a reasonable price. I got 1 from him last year.

Chris