My first computer was a hand me down Desktop AST 486SX-33 with a backplane for the CPU. This was supposed to allow for later CPU compatability, But the leap from 16 bit to 32 bit Pentiums made it irrelevant. No ATX stuff for me!
I did what I could with it. Evergreen 586-133 kit, added 256kb of L2 cache (it came with 0) STB Nitro 2MB ISA video card, and some kind of sound card.
It never would play games ( flight simulators) very well because of the ISA video bus. It may have had a VLB slot, but budget and lack of knowledge kept me from using that.