Let's see your painted engine/engine bay

I got hung up on the colour. I thought I was looking at Harvest Gold Caterpillar yellow. No excuse. I should have clued in on the HOLSET compressor. It is not like I have never seen a Holset compressor before. The company I worked for had over 1000 of them on Detroit Series 50s.
Compressor timing was something Cummins wanted and it is detailed in the shop manuals. Timing on a Series 50 was never mentioned. A visit from two Detroit Diesel Engineers changed the policy to timing the compressor, only when a new compressor was installed.

Your batting 0-2 that is an old Bendix 500 compressor (Guessing it's a 500, the 400 and 700 look similar). I believe the timing of the compressor was a hold over from when the compressor was not separate from the accessory drive, if you didn't time it when it was put on, all the timing marks would be off. When they went with the compressor that you could unbolt from the drive, it became less necessary. I wondered if the timing of the later type was to reduce the gear rattle in the timing gears at idle

I have nothing more to add.

Geoff, I can't remember which model compressor it is but I think you're correct on the 500. Here's a B/W, F-12 compressor that I've got to rebuilt next spring and a DD pump that are on another truck. Hardest part about working them is getting the chain back on.

I'm really not trying to pick on you, I just had to make the correction.
I'm not sure if Dan's engine was built that way or if the whole accessory drive set-up was changed if/when the engine was converted to PT pump system? I don't know or at least remember when the PT replaced to disk pump.

NikkI, if you look at the latest pic Dan posted, you'll see what I mean about the compressor not being separate from the accessory drive.
I'm fairly sure it is not a 700 pump, Dan those come with an air outlet on both top and side of the head, the smaller 600-500-400 could be spec'd with the outlet in either position, but it had only one outlet IIRC.
I have a 700 that I got for free, I ran it when 1st installed air start, but found it was not needed, so went back with a 501.

IDK, Dan, I would think lifting that big hunk and trying to bolt it in place would be too much for me anymore!

Geoff, If you look close at the top of the picture, you'll notice the bottom of a steel beam. I usually put a ratchet strap across that beam and support the pump while I bolt it on. The compressor is an F-12 which uses a lot of the same parts as the 500. Major differences are in the head.