Another distributor question

Bear with me guys, I'm trying to figure out what distributor would work for me and don't know much about them. I got a 70 340, need a distributor that I can adjust the mechanical advance. Looking at various aftermarket models but I have seen two different Mopar units mentioned on this website, one has the slots you have to weld and grind, which I have now and am not comfy tackling. The other seems to have a screw/tab arrangement. Are these distributors interchangeable? If if I wanted the screw/tab one, are they on small blocks and what years do they come on? Napa or O'Reilly or someone carry them?