I just broke down a 350 with a stock roller cam and lifters. The lifters are stiff and I can't depress them at all. I have another set of stock lifters and can I swap the insides of these lifters? Thank you much for your help.  

What year 350? How much time/mileage is on the lifters?

The lifters probably still have oil in them, so you probably won't be able to depress the plunger in the lifter.

Swapping lifter internals is really tricky if you've never done it before and don't have the right tools. If the other lifters you have are in good working order, why not just use those? That is if the lifters you pulled out are really bad. How does the wheel on the lifter look?  

The year of the engine is 1987, the milage is 88,785. The roller on the lifters look fine. My other lifters are flat tappets, and I was planning on using chevy zz4 cam.