lots to unpack here...
i'll start with the suspension stuff.
you don't *need* a V8 K, you can buy a swap kit and keep your 69 unit. it's fine. if you do, avoid 67 that's one year only with the "bad" idler arm mount. so 68~72 is all the same, as is 73~76 (though different motor mounts, but again a swap kit sorts that right out). the difference here being how the sway bars mount and their connection to the lower control arms. however, the aftermarket has you covered in that department with a whole host of options.
the rear end: 8.75's for a-bodies *only* came in small bolt, but can be upgraded to big bolt.
if you want to run big bolt, the you'll need to source another front brake set up-- stock 73~76 or an aftermarket kit-- and then all the attendant stuff that goes with it. not a big deal, but food for thought.
you'll need to sort our your column or buy one specifically for power steering. the manual column is longer than the power unit. they make adapters for this as well.
one benefit to the big bolt stuff is the availability of rims. but if you're fine with stock, stock, stock then small bolt has you covered.
on the engine side of things don't buy into the hype of "6-pack" stuff. most all of it was the same as standard 340, no need to pay the tax there. also 6 packs never came in a-bodies. 360 heads will do just as good as a job as standard 340 heads. you don't need a forged crank for the power levels you're looking at. selection of cam is at your discretion, if you want stock performance get a stock cam.