New frame rails?

Guys, my duster has a little frame rot on the rear frame rails where the frame connectors are welded in. Are the replacements from year one that say FRAME RAIL CAP, what I need to replace them with? Or are they just the crappy cover up-weld over the rust kind? I figure I might as well do it right the first time while I have the car apart to avoid future headaches. Are the frame rails spot welded in? How big of a pain is it to replace them? I have all the necessary tools & can weld extreemely well.

Thanks, Matt8)8)