atleast it isnt a Cummins N14. those things take forever to heat up.
but you have to look at it like this. the hemi, which is mostly aluminum and weighs about 550 pounds can heat up quick due to Al being a lighter metal. the Cummins ISBe tips the scale at 1000 pounds of iron. heating up that much iron takes a bit.
another way to heat up quicker would be to order the block heater pigtail and install that. every ISBe has the block heater installed, however in most areas the pigtail to hook up to 120vAC is a factory add on.
Shaun has the best fix. the air dams, which can be made from cardboard, can be used to force the engine to heat up quicker, and some have reported a fuel mileage increase from this in the winter. I guess it keeps the engine warmer to cause a more complete combustion.