well, I'll chip in a welcome to the garage, where you'll eventually find yer answers!
the 60-66 are all the same for the basic dimensions, so if you find headers/maniflods that are for a 66, you should be good to go - won't be much different twixt 6cyl and v8, as the trucks came either way - sometimes called 'the V8 era' series cuz v8's gained in popularity thru that period
got any wreckin yards around to look at for a 60-66 to see what yer missin? failin that, there'll prolly be someone here who can get a pic of their setup for ya - just keep lookin!!
Bill