If the plugs worked fine for you before, they should work fine with the MSD unit. The 46 is a couple steps hotter than the standard 45s, which I've always found to work great on mild street engines, but if the 46's worked for you, use them.
MSD distributors come from the factory with very conservative timing curves and totals, but since you bought yours at an estate you'll need to look at the springs and bushing in it to determine how its set up to advance. Just go to MSDs web sight or do a Google search and check their charts. The bushing you need to control total timing will be determined by the initial that you're running. Add your initial to the correct bushing to get your total. For instance, if you have 14* initial, you'll want the silver bushing that adds a max of 25* to total 39* (and maybe back off your initial by 1* if needed). If you're running 16* initial, a blue bushing will give you about 22* for a total of 38*
Typically, you'll want the timing to be "all in" by 2800-3000 rpms, so that would call for the blue springs if using the blue bushing (16* initial), or one "light" silver spring and one blue spring if using the silver bushing (14* initial). These are just examples but should be close to what you'll need. The beauty of the MSD is you can play with them so easily and see what works best.
I THINK you need the tach adapter for a factory tach, but I'm not 100% sure on that. Make sure you check it out for sure because I think it will burn out your tach if you don't.
Yes, you'll need to remove the resistor. MSD's don't require them.
Here's a shot of MSD's spring/bushing chart.
