If they have Pentium I processors (60mhz - 166mhz) then you would be able to put in a Socket 7 processor such as the K5, maybe a low end K6 in the board so long as the bios supported it, but back then AMD were a cheaper option, Intel Pentium's were superior in performence.
I wouldn't bother doing much upgrades to Pre Pentium II/AMD K6-2 machines, unless you have a load of old hardware to play with.
Corm