I bought a book for the Bonneville this weekend, it was from years 1985 to 2002, and it really wasn't specifically for the Bonneville it was for GM full sized cars including Pontiac. Which I know is a GM. Anyway I was noticing that some of the older Bonnevilles had headers and a strut tower brace. I think you know where I am going with this, but I will ask anyway. Will those components work on a 2000 SSEi?
The headers won't. Our valve sequence and spacing was different. They're more of a tubular manifold than a header anyway. All Series 1 have them. L27 and the Series 1 L67.
I know the STB will fit the 87-91 Bonnevilles if you steal one from a 92-99. Being an H body also, the spacing should be the same, but the tower height and other goodies being in the way might be a problem. The STB itself is VERY inexpensive, even brand spankin' new.
There are also plenty available at salvage yards. You should be able to pick up a 'test' bar for a mere 20 bucks or so. New isn't much more.