Thanks for the post. That came up on my initial search, and I don't really trust it... it seems like they're feeling around in the dark. All the gauges and senders I've come across are measured in ohms of resistance, not volts... unless LS1 sensors are different, which that post really doesn't suggest. It does suggest that the sender functions in the same direction as the gauge I'm trying to match, so that's a start.
Somewhere out there, somebody made a chart of stock (not aftermarket) sending units, and I want to see what the values are for the LS1.
I might call Street & Performance tomorrow. They're pricey, but they seem to have every specialized part you can think of for the LS1... and then some.