they are normaly set up with a much lower MAX rpm than the road engines.
some where around 2,600 3,000 rpms
Isuzu diesel road engines are around 4,250/4,400 MAX rpms
you can fuge not having a road IP but it will be rather funny to drive, any time you give it go pedal you will be at WOT or very close
but the lower max rpms, will peg you out at a very low speed, as low as 40 mph if its 4.55s with a 4 speed and 24" tall tires
change to 3.73s and the 14.5% O\D 5 speed, you can go just under 70 at max rpms, with 26" tires
will not be very good mpg having to run it that hard.
with the 3.42 gears it would be over 70 a little, will get good mpg at around 55 with 3.42s but 1ST and reverse will be insane tall.
my calculator
http://www.izook.com/gearcalc.htmso yea as stated before, can be done, but not a good idea for the road.