I have 1979 blazer and i need to replace the front driveshaft and in my area they are hard to find what i need to know what years will enterchange with my blazer I have full time four wheel with an np203 transfer case
I would assume that you have a TH 350 trans. That makes a difference as well. With that said, any truck that also has a TH 350, and the NP 203 will work. The problem, is that 1979 was the last year that the NP 203 was used. Your best bet is to have yours rebuilt. Call some driveline shops, they should be able to help you. I just got a rebuilt front shaft for my 80 GMC, and it was $263.
One of our parts stores here used to be able to get new driveshafts, complete with all u-joints and the price was amazingly low. You might do well to check parts stores in your area and see what they can offer. Particularly so in the case of a GM front shaft where the Cardin joint could be going bad on a used one.