Yes a Rev a Machine can be upgraded to Rev C...mostly. You can swap in a Rev C ROM which will fix a few things. The only thing that won't change is the on-board video.
I would highly suggest a CPU upgrade as well. ZIF's are cheap and plentiful. A step up to a 500MHz G3 with 1MB of L2 cache will make that machine much, much faster.
If you do both upgrades it will be faster across the board.
You could get really crazy and install a PCI ATA/100 Controller. Then your boot times, app load times, install times, and pretty much everything that access the HD will decrease by a rather large margin as well. ATA/100 are cheap and plentiful. A 40 or 60GB drive in a machine like that would be a breath of fresh air.
With those 3 upgrades in place you would have a decently capable Panther or Tiger box.