If you weren't aware, there's a company that manufactures brand new replacement feet for the Quadra/Centris 610/PMac6x00 line and they sell them on eBay. A set of 4 are like $25 or something.
Alternatively, Performa 611x Macs often sell for very little on eBay for some strange reason. I picked one up recently with a CD-ROM, 16MB of RAM, a working 500MB hard drive, and case in excellent condition, for $20 plus $15 shipping.
Some OrangePC cards (486) have built in video and have a dongle out the back for connecting a monitor directly to the card. The 386 cards I own use the Mac video for display.
Decent 1 came out in 1995 which was socket 5 Pentium 1 era not 386. The game does not need a 3D accelerator, nor were ANY ISA cards made to accelerate 3D. The best you can do is use an original Voodoo 1 (PCI) with a beta driver to play the game accelerated.