how about mount the compressor pump to the existing plate.
Then install the motor hanging over the edge on an adjusting pivoting plate. Install a bracket from the plate or the pump to hold the tension on the motor. With the weight of the pump on the plate I don't think the motor hanging over will cause a problem. If it does then bolt the compressor down
The other option I like is mount the motor and pump separate. You can put them under a bench or in an enclosure or something. Then put the tank outside
Bob
I do like that idea. However instead of a pivoting bracket (i'm picturing old alternator) I would do a sliding setup with a bolt to add tension to the belt/s.
Unfortunately tank outside won't work. Well, I was ok with it. Wife not so much. Here's the original tank. Was a 120gal.
Whoa! That's a heavy compressor for a vertical. Make sure the tank is very secure. Congrats on that Dresser. You won't find anything better, even a Quincy QR.
Yea, its pretty massive. The vertical sections on the top plate are 5" and its 3/16 I believe. I need to verify that. I should just model it out and run some fea on it. Looking forward to it though. Haven't heard a bad thing on that pump.
Was a package deal. The ad listed the extra compressor but was a bad pic. When he said the plate read 660A my eyes got real big. The other is a Kellogg 452. As long as the Dresser is ok I'll resell that Kellogg since dad didn't want it. Guess he's fine with his 3hp Northern Tool.

He doesn't appreciate the old iron.
That's a lot of pump, what 250 lb? Be sure the new top plate is stout enough. There was a compressor assembled from parts done here. frankenpressor, maybe? Been a few years but they added a few plate extensions to the side for the motor. Good luck!
The data sheet lists 270lbs. Not sure if that includes a pulley. I sure as hell can't pick it up though. I'll have to do a better search. I think I can get it setup to support and balance the weight ok. Just not sure what kind of reaction force its going to put out when it starts running.
What I did and what I would do in your shoes. Mount the tank on a shelf up on the wall ~4'. Then build a skid for the compressor/motor assembly a foot or so off the ground. Just make sure you have a drop leg between the compressor and tank so moisture won't run back down into the exhaust valves.
That would have to be a pretty decent shelf. Especially in a garage. If I went that route I'd rather add a shelf above the tank for the motor and pump. It'd be nice to keep all the belts and pulleys away from stuff that could get in them.
I'm kind of leaning towards adding a new top plate on top of the existing. Essentially taking the inverted C channel and placing a larger length over it to sleeve it in a way. Then can weld to the existing top plate. It might mean I have to run a bolt through two plates to mount the pump but longer bolts could fix that. That would help beef up the strength and allow me to fine tune the position of everything for the best weight balance. The motor i'm looking at is 134lbs.