As is said quite a bit around here, they are worth what you are willing to pay for it. You do have a couple of things going for you, and Tim can probably confirm this but it looks like a deluxe cab with the trim around the windows, the grill looks straight which you don't often find and the hood and doors look ok too. The steps on the other hand look like there isn't much left so will require some parts hunting to replace.
Just my opinion but I think $1500 is too steep. If it sets there too much longer it won't be worth much to the guy and scrap value could only be what, $100-200? Let the guy know you are interested and see what his bottom price would be.
There have been many conversions were these cabs have been put on late model running gear from half ton all the way up. One issue with going with the s-10s and smaller trucks is the tires often look too small in those big wheel openings. That may not bother you though. Also the earlier trucks had narrower WMS to WMS compared to a lot of modern trucks causing the tires to stick out a little too far. Again this may not bother you. I'm just saying. If you do some searches and check out the Tech Tips, there is all kinds of info on tire, wheel and brake upgrades for big bolts.
Keep us posted on your purchase and good luck!
