There's been some discussions that referenced installing a later engine in an early C180.
My own 53 model has a K engine, but retains the stock mount intended for the A or J engine.
Field approvals were obtained to install early engine mount legs on the later engine,
as well as to install the modified engine on the airplane.
Done that way to save money, I guess.
I have been surprised to find out that a number of other early 180's with later engine have the same set-up.

I never heard of doing it the other way around-- putting an early engine on a later mount.
But I was poking around on the Seaplanes West website recently,
and found what looks like the very first service letter Cessna put out for the C180 which addresses doing just that.

That is interesting. I have the K with the original A engine mount. Didn't do any 337 since K was on the Type Certificate which says A J K.

Yep, the A, J, & K engine are all on the TCDS for the 180.
However, revision 34 of Aircraft Specification 5A6 says the K engine installation
in a 53-57 180 must be "per Cessna dwg 0750200".
(FWIW my copy of the TCDS is revision #63 & it does not seem to include this)

Now I don't have a copy of Cessna dwg 0750200
( if anyone's got it, I'd sure like a copy)
but I'm guessing that it shows the later p/n 0751001-1 mount.

I think the putting the early engine legs onto the K so you can use the J mount
falls into that major or minor alteration / field approval required or not gray area.
The guys who did mine figured a field approval was required, you & your guy(s) didn't.
Both valid positions.

delete

And then there are all the Pponk's out there with the early style mounts. Wonder if mount is even mentioned in any paperwork?

My engine is pretty high time, I'm probably looking at an overhaul sometime in the next couple years. I plan to swap over to the -1 470K engine mount, and install the aluminum seaplane bushings where it bolts to the firewall.
I'm gathering stuff as I go, already got a set of the later crankcase legs & barrel nuts for bolting on the rubber isolators.
Speaking of which, any opinions on using Barry brand rubbers instead of Lord?