Welcome!
It's a stock CD player.....just not for your car. That's a mid-'90s Chevy radio. Don't know off hand if it'll work with your steering wheel controls, but I'd venture to say yes since the Gen 1.5 Monte Carols came with that same stereo and a black version of the same steering wheel controls. Unfortunately, the lights will be the Chevy white.
WHAT?!? That's the best part of Gen I w-body GPs!! I'm partial to the '89 - '93 style body kit, but I love the '94 - '96 as well.
I'm glad you know enough to do that. The LIM gasket is really the only weak link in these motors, and is the cause of the early demise for most of them. Other than that, the 31/400 is bulletproof.
Yes and no. If you're going to dive deep enough to do the LIM, and especially the head gasket, I'd swap the top end out with a 2000 & up 3100 or 3400. They flow much better, and will net you around another 15hp/10ftlb of torque. Yeah, it's not much, but if you've already got the top end out of the way...
The body kits have been available since '89 (with the TGPs), so year is irrelevant. The B4U (the body kit's RPO code) package is just added on to the same body as yours with the exception of different front and rear fascias. However, it's MUCH easier to get parts off a car that already came with a B4U package so you don't have to worry about drilling holes in them for the clips that are needed to install the body kit.