Newb Questions

Truck-Magnums have dual mounting pads, but the truck bosses, I am told, will interfere with header selection.
Per a recent discussion here on FABO, 67 to 72 headers, and Schumacher adapter-mounts on a slanty-K, do Not play well together.
IMO;
Your best bet is to find a 73up V8 A-body or similar vintage chassis, and transfer all the required bits over from it. The LA family is not to be feared. If you are opening the engine up anyway, then the only advantage might be the roller-cam, which to me is relatively meaningless.
Your slanty, besides a cid deficit, mostly suffers from a lack of rear gear and stall. For a city-only type combo, this is easy to get around/overcome.
I have a 70 Dart slant 6 k member, Schumacher conversion mounts, 360 magnum, and Doug's D453 headers.
I'm guessing the discussion you referenced was using inexpensive headers that the steering linkage passes through. The only clearance issues for me are the tubes very close to the ps box, which I solved by raising the engine 1/2 inch on the driver's side. Yes, I realize quality control from the factory was poor, and that what fits one car may not fit another. I was under the impression that all 360 magnum's were "truck" , that is installed only in Jeeps, and pickup trucks ???