Yes. You get the higher clock speeds by increasing the multiplying factor. Not by increasing the bus clock speed. In theory, it can be done either way, but the bus speed isn't going to work past about 60 MHz, and without knowing how to set the CLOCKID pins on the CPU socket, it may not work much above 45 MHz.
The PPC740 and PPC750 had clock multipliers up to 8X so there's plenty of room using higher clock multipliers.
The difference between the 740 and the 750 was that the 740 did not support the L2 backside cache and so did not have the hundred or so pins needed to interface with it. This is what made it possible to be pin compatible with the PPC603 (?) which (of course) also had no pins for a backside cache.