From what I can tell from the wiring diagrams that I have, I think the only thing that doesn't run off the PCM as far as gauges go is the oil pressure and voltage... Everything else is carried on a serial data stream from the PCM...
As for the oil pressure, check out this thread from LS1tech.com, the #3 post by
Mr_Dude 1 seems to indicate that the LS1 sender works well enough with a 3rd gen gauge. I would assume, then, that it would also work going from a SBC sender to an LS1 gauge...
As for voltage, there are no specific wires for the voltage gauge on the connector, I would assume that it is wired up internally from one of the +12volt sources to ground.
Keep this in mind. I don't remember what year my LS1 cluster diagrams are from (except that they aren't '98) and the two other threads I used for reference seem to be using '99 clusters. Now, I have no real reason to think that a 2000 cluster pinout would be any different, but I also can't say for 100% sure that they are the same. So, with that said I would just make sure that when you are doing the wiring to check for any discrepancies, like wire colors that don't match. Also, if you have time and access to factory manuals to source your own diagrams I would do that. But, then again I am fairly obsessive and my public library has a good collection of factory service manuals...
Anyway, here's a few links to some pinouts (both are 99's, I think...) This is the
one that talks about what stuff is carried on the serial data stream, and
this one has a picture to show the cluster connector. Both are from
LS1tech.com, which you should check out if you haven't already, they have quite the collection of info, but it usually requires some searching to dig it up...