I'm in the process of replacing just a head gasket in LS1. I removed the head, haven't touched valve springs or cam, but I removed a plastic valve lifter guide and 4 valve lifters(which is a unnecessarily step that I found out later).
the problem is, I might have put the 4 hydraulic lifters back in wrong order. will this cause any trouble?

 

Do you mean the original bores that they came out of? It wont make a difference. As far as orientation the oil holes point toward the center of each bunch of four.

 

thanks for the reply.
to clarify, I removed 1 plastic valve lifter guide and 4 valve lifters in this picture, and I think I reinstalled the lifters in random order. (I haven't touched the valve springs)
are hydraulic lifters in LS1 identical? do I have to adjust valve because I put them in wrong order?

 

You'll be fine with roller lifters. The reason you can't move them around in a flat tappet motor is because the "old style" lifters actually wear themselves into their corresponding cam lobes which necessitates they go back where they came from. Not so with rollers.

 

Exactly the flat tappets establish a wear pattern on the cam that is unique. Rollers just roll on the lobe so no pattern is made. Thats why guys are always buying and selling used ls cams on here.