Upon digging a little deeper on your question, due to curiosity:
Here is a link to another thread from some years ago that goes into good detail on several of the engine codes we have been aware of, and some pictures of where the code stamping on the block is located.
https://d24t.com/showthread.php?t=324
On the second page of that thread, note this post (which contains a dead link but mentions some info from the linked site):
Quote:
Originally Posted by 745 TurboGreasel
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So there's your GR code, sounds like it is a real code that is for a D24T.
It might be a later type D24T code, since we never saw this code here in US where sales of D24T ended in '86. Maybe intended for use with a later style hydraulic lifter cylinder head that you probably have, as opposed to our mechanical heads that were present on the engine codes we have seen on these shores.
Also, since the info quoted above suggests that the GR code might have been used in Volvo cars rather than LT trucks, one possibility is that your camper had a Volvo engine swapped in at some point as a replacement for the original engine. Do you know if that is the case? Did it start life as a NA D24 rig and have the TD engine retrofitted later? If you aren't sure, it might be possible to figure this out by seeing if there is an unused (maybe blocked off) dipstick hole at the bottom of the block on the left hand side. A TD engine from a Volvo 740/760/940/960 would have had this dipstick hole but AFAIK an original LT spec D24T may not.
In any event, it's probably the case that for purposes of ordering repair/maintenance/overhaul parts the GR will be more or less interchangeable with the other D24T codes (DV, DN, NY, etc). It seems like most of the differences between the various codes have to do with external components like the location of hose connections, dipstick, etc. The only really important mechanical running changes to be conscious of are the use of early mechanical vs later hydraulic valvetrain, and then a redesigned timing belt/water pump system that was used for a short time on very late production engines in the mid 1990s onward.