Operation /6 - Where do I begin? Fix it or yank it?

Don't fret, you only learn by doing and this isn't a tough job. It would be smart to get a manual though (factory or Haynes).

I don't recall ever doing it on a slant, but I expect the same as my small and big blocks, which I have done. The lower sprocket should just slide off. It isn't pressed on, but you may need to spray WD-40 and a little wiggling to free crud. A simple puller could help, especially if rusted together. You need to slide the two sprockets and chain back on together, since the new chain is tight and things will barely fit (good). There is usually a step on the crankshaft which helps get it started.

Re clocking, the two dots on each sprocket should be next to each other, both on a line between the 2 sprocket centers. At that point, the #6 piston should be at TDC on compression stroke, with #1 at TDC on exhaust stroke. You don't really need to check that since "get 2 dots together" is the only rule you need. I just mention it since it most people ASSume that it should be #1 at TDC compression (I did). Custom timing sets often have multiple dot sets for special settings, which can be confusing, but I haven't seen that for a slant and probably not at the $30 price.

As mentioned, I think you need an "oil slinger" on the crank. At least SB's have that, though I don't recall one on my BB. For sure change the front seal. It is easy to beat out with a hammer & screwdriver, but support the cover well so you don't bend it. Use a big socket or similar to knock the new one in. The seal should come in the "timing gasket" set.

Finally, this is an opportune time to consider changing your camshaft and lifters. It would be a shame to have to do all this again if they are worn out. If you have the removable spark plug tubes (I think 74 does), you can remove the lifters out the top with the head on, by just sliding your hand down. I would pull the valve cover and pull each out to inspect. If shiny on the bottom and no rough spots or grooves, they should be fine.