Engine with multiple serial numbers

I've been working on swapping engines in my D4 with an HT4 loader attachment. The previous owner neglected the machine and water found it's way in rusting it up good. Today I was swapping out oil pans because the one that came out of the machine is different from a standard tractor since it doesn't have a oscillating spring and Instead it's a big solid bar tying the track frames together so the notch in the pan is much wider to cradle it. The donor engine is from a numbers matching D4 6U8892 but what's strange is that when bolting the pan on I noticed there's another serial number stamped in the block just below the lift pump and it's 7U25462. I'm curious if anyone has seen this before?

I couldn't tell if the pictures loaded so here goes again.

I myself have never seen a third matching serial number for a machine; In some instances, I have seen numbers stamped in the same general area for possibly a re-builders job # or reference. I think Mr. Old Magnet wrote something about numbers stamped along that spot at one time. Maybe he will take a lunch break and see your inquiry? I have yet to know why sometimes a tag will have a "Z" stamped into it!

BTW: you are deep into that swap. Tight quarters there and not nearly as easy as a bare machine. Hats off to you and your revived line of machines. JM

Thank you Juiceman. The donor engine is from the D4 I picked up at your place last year that I purchased from TractorDon, I should ask him about it and see if he knows something. It's kind of funny that the number I found on the block 7U25462 is being transplanted into a D4 7U25155 because those numbers are only weeks maybe months apart if I had to guess. I actually got the engine set in place today all by myself lol, I do everything by myself so nothing new except this one was pretty challenging. Fortunately the machine is in pretty good condition overall and the steering clutches are free so I should be able to get this old beast up and working next week. I'm waiting on some orings and hose for the hydraulics but have plenty to do in the meantime not just reconnecting stuff but there's a bit of welding to do because I had to take the torch to the grill mounts and other stuff in order to get the engine out.

Nice HT4, but you just HAD to let your new Chevy pickup truck sneak into the photo! Some people have all the luck! JM

I wouldn't have the truck or the four RD4s and the load of other goodies I just brought back today from the nice widow lady if you hadn't enabled me 🤣.

Seriously though JM, thank you for sharing her posting of that first RD4 she had for sale. Here's a photo of it on the left, it's a really nice machine and definitely one of my favorites. I did get one of the other RD4s from her running but it needs some work and the other two are pretty rough but I should be able to get them going again.