I just put a new HU in my wife'* Bonneville last weekend. I used a multi-fit kit, similar to the second one you show. I had to wing it a bit, as the instructions didn't have the bracket settings for our '94. But by setting both the old factory unit, and my new one in the mounting bracket, i was able to find 3 of the enclosed brackets that I could make work. I thought it turned out really well, I will have to try and remember to snap a couple pictures.
So far I am just running the new HU thru the stock speakers. I have not purhased the interface to regain use of my wheel-mounted controls, that is next on my list. Then I will worry about speaker upgrades.
I used the same multi-fit kit in my *-Blazer, and was very impressed by the way it worked, and it'* final fit in the dash.
That illuminated one sure does look cool, though.
I'll have to settle with my install, and the $9.99 dash kit I bought, though.