there are some small things, you can put 73-87 front under a 64, the steering box ( usually) needs to have a hole cut in frame then plate from backside welded in for clearance issues but you can just use a spacer between the Box and frame ( if you use a spacer it will turn real sharp one way and not the other), the rest of it bolts right up ( been a long time but ya might have to drill a couple holes, not sure of that). you need preporsioning valve for the disk brakes and you will need a DUAL master cyl not the single for the 64, to get the 5 lug in the back use a 70-2 rearend for the trailing arm setup. on other things, the Trans crossmember from a 70-2 th350 truck works after you drill holes and you can take the Bellhousing crossmember out to run easier exhaust. I have built MANY 60-72 chevy pickups. Also when ya put the 73-87 front crossmember in you can use the 73-87 motor mounts and use 350 manifolds instead of kicked back Centerdumps that always break on those trucks and if I remember right it also moves engine forward so an HEI will fit in there. If anything else comes to mind I will post more
Jim