I am currently upgrading my IBM P70 portable (386-DX20 with Math Coprocessor and 8mb memory) and so far have added the following:
Working 3 1/2 floppy drive from a model 25 286 parts machine (P70's are notorious for bad caps on their floppy drives)
Backpack Parallel Port CDROM drive (Bought on EBAY for $15 with non working drive. Replaced with CDRW)
386 Enhanced MCA Memory Expansion Card (has 12MB on card to go with 8MB on motherboard) (pulled from Model 70 desktop)
OPL3LPT Parallel Port Sound card
TI 486DLC -33mhz processor (Bought on EBAY for $10 shipped to door)

So far everything is working including enabling the cache on the TI 486DLC-33 processor although it is only running at 20mhz since the Xtal for the CPU is a 40mhz crystal. I had noticed when i bought it that the Math Coprocessor was also rated at 33Mhz so I have ordered a 66MHz DIP 14 crystal to replace the onboard 40MHZ one which will hopefully bump up the speed to it's rated 33MHZ. I have also bought and installed a heatsink for the CPU (Blue to match IBM) and was wondering if anyone has ever tried to overclock a DLC processor before. Would trying an 80Mhz crystal be worth a try next bumping it up to 40mhz since it now has a heatsink installed?