As for camshafts and bearings. The cam journals are the same but the journal bores on #5 in the blocks are different in the 99-00 truck blocks. This isn't widely known because the early Gen3 4.8/5.3 truck blocks were usually scrapped before the LS craze caught on. Besides, there was more call for actual LS1s or 6Ls back then. But the bearings were thicker which maintained the cam journals remaining the same. Why GM did this...who knows but I hope they fired the dumbass that designed that part.
Hence I'd seen where a guy jammed the larger bearings into an LS2 block. They kinda fit but the cam wouldn't go in. LOL

 

I used to have a 5.3 block out of a '99 Silverado of mine. My local machine shop accidentally destroyed a tap deep in a cylinder head bolt hole when they were chasing theads. That's what they told me anyways. They found me a replacement "LM7" block. I'd love to know what year vehicle it came out of but it's a mystery. Does anyone know of a way to read casting numbers to determine any valuable information about this block? I do know this new block uses different head bolts (all short) and does NOT have timing chain guide bolt holes like my '99 LM7 block did.

 

if it takes all short bolts then its a 04-07 classic truck block, i dont think the casting numbers will tell you the model year..might be able to check the VIN stamping on the left side of the block to determine that. If it has the rotating assembly still in it that could also give you an idea. The 2005 and up are considered gen 3 1/2 cause they used the newer better rods.

 

I don’t have a rotating assembly. Correct me if I’m wrong, but the casting digits are 24L05 and I suspect this is a December 24, 2005 casting. My original block was a L058 (December 05, 1998) I have no proof I’m reading these correctly.