Yup that's where mine sites even with Lund grille sections in place and the radiator covered save for 1.5" on each side. The cooling systems are pretty robust on these trucks. Does the 203^ stat put temp mid range on the gauge?

j

 

My 203 stat with fresh coolant in it sits at the "r"

 

I figured that would work. Thats good news. As far as hardware goes, any hardware store probably has the right size, just bring at least one if the old ones with you to check. As ithers have mentioned on here, you cant just throw any thermostat in there. I actually just bought the same one dieselsite sells, the 203 long stem for my 97, but from a different place. From what I have read through, you need the long stem one if yours is a 96+ because of the coolant bypass valve. I have read that if you put a short stem thermostat in it will still work but temps can get super high in the cylinders in the back of engine and you won't know it.

 

mines a 97 obs

 

Hate to tell you it's not that it's a "good" cooling system, but your stat is bad.
There may be some flexibility in the dummy gauge on the dash, but I've been there, done that. If it's not in the "R" range, the stat is bad.
I had a truck years ago (the one I mentioned previously) that I covered 3/4 of the radiator with cardboard to try and get some heat out of it in the winter. It still wouldn't heat up. Only when I installed a new stat would the truck reach operating temps.