I'm not finding anything with the numbers you have given, but what I am finding is that we should be looking for a 6 digit number, starting with a 3 (I think) if the engine was built in '79, or a 0 if the engine was built in '80.
Any chance you could post up some pics of the number on the block?
BTW, this is what I'm referencing for the block numbers. (You might have to click "proceed to link destination"...)
I should have been more precise about the CJ. It's not mine, and I actually don't have it in my possession at the moment. I have a Jeep/4X4 shop & the owner is a new customer who doing a lot of work himself. I haven't seen the numbers in person, but he wrote them down & brought them to me.
He & I looked at an '85 CJ7 258 block I have on the engine stand in the shop. It has 6 digits on it, and we both agreed that his block seemed a digit shy of a full number, but he was certain that he copied down correctly.
Also, he mentioned that the stamping on his block was much smaller size print than the one in my shop.
Unfortunately, I'm not going to be of much help if that is the case. I tried to find the number you gave a few different places online, but to no avail. Hopefully someone more knowledgable will drop in and enlighten us.
1984 jeep cj7, 258 I6, rebuilt T176,rebuilt Dana 300, amc 20 , dana 30, 4.10's Trac-lok in rear , 4.10's detroit soft locker in dana 30, 2.5 inch bds suspension lift, 1 inch polyurethan body mount lift. Line ex. weber carburetor. factory tach. factory clock ,oem replacement speedomter cluster, and oil pressure gauge, factory volt gauge.
I think that's a build code for a newer version 258, of the 4.2 era used in the YJ. I think the decoding sites already listed only go up to the mid 80's. My guess is it's an early 90's 4.2L/258 from a YJ.