Weird, I took a look at the ROM on my 270c. Usually drivers are DRVR resources in the main ROM. The 270c has the following drivers:

.Backlight, .Sound, .Sony, .MPP, .ATP, XPP, .netBOOT, .ATBOOT, .EDisk, .BCScreen, .ENET

I don't recognize .BCScreen, but everything else seems pretty normal, I'm not seeing an obvious driver for the data pump. Perhaps it's not really a driver in the normal DRVR sense, but a set of routines somewhere following a different layout convention? Or gets loaded through an onboard declrom somewhere.

Also, .AIn, .AOut, .BIn, .Bout are the normal serial & printer port drivers, but I don't see them in ROM either.

FWIW, I'm using ROMmie, which is a pretty nice tool for extraction, it includes both a dump of the ROM and parses out the resource data into a .rsrc file suitable for use with Resedit or Resorcerer or similar.