I didn't do the math earlier.  If you disk is larger than 1Gig, look to 
see if the 1542 is new enough to support "disks > 1 gig".  If this
option is enabled then the geometry is, 255 heads and 63 sectors.

NOTE: you can not tell netbsd that your disk had 255 heads.  Instead report
you have 51 heads and multiply the number of cylinders (you calculated
by dividing the capacity by 255*63) by 5.  This means that the offset to
NetBSD (if non zero) would also be multiplied by 5.