Skip the Autolite plugs (Chinese junk). Tune-up parts and technique suggestions, including spark plugs, are in
this thread. The engine may well be overdue for a
valve adjustment, too. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted
here for free download.
Once you've got it tuned and adjusted so it's running its best, there are lots of upgrade options. You'll hear the name "Clifford" come up, but be very careful before you decide to spend any money with Clifford. They have a long and ugly reputation for being a bunch of clowns; see for example
here,
here,
here,
here, and
here. Much of what they sell is inaccurately described, and a lot of it is not even slightly cost-effective. The good news is that you don't need to go to Clifford to get hot rod parts for slant-6s; there are lots of other, better options. See for example
Dutra Duals and header options discussed in
this thread and
this one,
Erson custom cams,
HEI ignition upgrade,
Mike Jeffreys windage trays,
Hurricane intakes,
other exotic intakes. Hi-perf engine buildup
here, high-perf parts and build info
here.
