Pretty good article as far as giving an overview of the three common types of m42 thread-mount lens aperture control systems.
IF on the chance the OP is still around...I would say that if he wishes to use grandpa's old lenses, a mirrorless camera, or a Canon digital SLR would be much better choices than a Nikon d-slr, due to the flange-to-focal-plane registration distance issues involved. Canon d-slr's, inexpensive used models, would enable
glass-free adapter use. Still...28,55,135 lenses from that era are typically not all that handy to use for the beginner or intermediate shooter...the convenience of AF, the convenience of automatic aperture control, those things are very worthwhile for most people.
I've found that shooting older, adapted m42 lenses (Pentax Super Takumar models mostly) on my Canon 5D was an okay, and fun experience, but rather slow and also hit-and-miss as far as focusing was concerned; not nearly the same hit rate on focus with an older, adapted lens as with say, a modern, AF lens. The utility of adapted lenses depends on what one expects to achieve, photographically, with the lenses. DO you want to take the 135, mount it on an APS-C body, and have a 135mm x 1.6x effective angle of view? Well--you can GET THAT with a used Canon Rebel d-slr. But, do you want to get shots of kids playing soccer, IN-focus, on shot after shot after shot, all game long? You'll probably NOT be able to achieve anything better than say, a 50% focus hit rate. But, if you want to walk around, and shoot shots of zoo exhibits, or landscape shots, then the slowness of focusing by hand-and-eye will be acceptable, and the success rate ought to be 90% or so, with the standard focusing screen in the camera.
