Some additional information from my Rolair rep for you:

The K28 has the same footprint as the K24/K25. We do not have any manuals that old. I'm not sure who he talked to here, but it seems a little odd that they are so confident, unless your customer gave them some casting numbers that we were not made aware of. I have included our Chinook pump manual, the K24 breakdown, and the Chinook 2 stage spec sheet.

I hope this helps, along with the attached documents.

- MTR

Usually the casting numbers are on the upper portion, on the finned sides of the crankcase. On the cylinder, it is usually on either the lower flange, or in between the lower cooling fins.

- MTR

Here is my take on using older air tanks:

Old tanks normally will pin hole out eventually rather that catastrophic failures as long as they have a good working safety valve in place.
But there is always that one exception and who wants to take that kind of chance.

The serious accidents happen when safety valves have been plugged off and a pressure switch or starter contact points get stuck.

Tanks that have been in constant use are normally considered safe, because they rust slowly to a pin hole state. But tanks that have been left in storage can be a lot more risky as the rust can be over a large area weakening the bottom. Constant use tanks also have a film of oil and that helps reduce rust inside.

The other failure for tanks is vibration stress cracks. Usually at welded corners of the top plate and legs.
People will be tempted to weld on those cracks. That is a major hazard for sudden failure.
It is illegal to weld repair ASME tanks unless sent back to a ASME facility.

- MTR