I don't see a problem with the alternator or the PS, as long as they'll mount to the BB brackets.
(Also assuming the alternator kept up with whatever equipment you already have.)
Never heard of PS pump in that era interfering with a K-member.
I had a BB Duster with a 26" radiator swapped into it, using the original rad support (not opened up), wasn't a problem.
18.5" is a large fan, probably not necessary, but by all means use a shroud.
I'm pretty sure all Mopar clutch-fans interchange as far as the 4-bolt pattern to the clutch.
There's also the Jaguar-spec shorty clutch, or just run a direct fan (for what I guess is a street cruiser).
Should be fairly easy to find an OEM shroud that'll work.
Speedway sells a universal fan shroud, roundabout $50, but you'll have to make brackets.
Air cleaner - look for a drop base (Ebay, Amazon, Summit/Jegs/Speedway) and run that under your stock setup. You may have to play with element sizing (ID/OD/height).