In a nutshell all of the pulleys and brackets have different offsets...As previously mentioned you'll need the shorter water pump bolts...but everybody forgets the difference in the size of the bypass hose...Cast w/p is smaller by a bunch...

New pulleys...alternator brackets and spacers...bypass hose and a belt should be all that's needed.

The pulleys you need will be from the earliest 318 poly motors up through the 273-318 and 340 until 69... Staying away from any A/C equipped cars...