Engine rebuild practices question
 

When I bought my Fuso FG it had no service records. The engine block was not painted and had some light rust on it. I suspected that the engine had been replaced. In looking at the engine number today, it appears that some numbers have been stamped or ground into the plate on top of the originals The initial numbers are the same 4D34 but it looks like G9 was added afterwards.
Does anyone know if it is standard practice to renumber an engine upon a rebuild? G9 is definitely not part of the original engine number on the truck's information plate. It looks like G9 may have been ground in with a fine tipped dremel tool.

I am not sure if there is any national law that touches this.
Practice varies.
A friend has a '38 Ford with a Ford Authorized remanufactured engine. Engine was assigned a new Rebuilder's Number on a plate riveted to the block.
Mt '82 300SD has a Mercedes replacement engine, installed at about 100,000 miles. It has a different S/N ( stamped into the pad on the block, which identifies it as a factory-built replacement.

Would a CarFax check run on the VIN show the engine replacement?

Good question on the Carfax. I don't know. I'm pretty sure the vehicle spent it's whole life as a fleet vehicle for Sunbelt rental before it was sold off and I bought it from the wholesaler. I'm also pretty sure the wholesaler didn't do any mechanical work to it.

Here's an interesting development. On a whim, I googled Sunbelt Rentals which I suspected was the original owner of the truck. They were selling another truck online. I sent an e-mail to the addressed listed, explaining that I owned what I thought was one of their former trucks (gave the VIN #) but had no maintenance records, asking whether they had any. I got a nice reply indicating that they had the maintenance records in their computer and if I gave them my address they would send me a copy. Quite surprising in today's world.