You'll be okay using everything except the K frame and centerlink/tie rods, and sway bar if so equipped. Those parts are all different widths.
You'll be able to use the upper and lower control arms, spindles & brakes, torsion bars (make sure you're at least getting basic smallblock V8 torsion bars or better), and a few other odds & ends; although they're pretty much the same parts as '65s (unless your intent is to upgrade from, say, 9" brakes to 10" or discs).
That knocks down the list of early A only parts you'll need to the V8 centerlink (it has a dropped center for oil pan clearance) and motor mount brackets. Your K frame is the same as V8 units. If you want to run a sway bar, you'll also need the early A unit; but the lca sway mount tabs remained in the same location until '72.
Another useful upgrade would be to grab the dual-pot master cylinder and proportioning/distribution valve and associated lines from the '67 and use them in your '65, getting rid of the single circuit unit you have.
I hope you got a transmission with your 318; the slant 904 (if automatic) or bellhousing and flywheel (if manual) is different between slant 6s and V8s. If automatic, you'll also need to deal with linkage differences, as the '65 and earlier use a two-cable shift mechanism and a ball & trunnion output and driveshaft, whereas '66 and later use mechanical linkage and slip joint output and driveshaft. There are also speedometer drive and cable differences.
