Fully assembled (body) partscars, ESP ones out of the same asm plant, same time of year as what one is restoring, can be a very valuable resource of where certain bolts go, types of plating, how ducts and wires are routed, etc. If the partscar fits that criteria, and you're pursuing a very high level restoration, take tons of pics, bag and tag all the under hood bolts. If you have the room, you may want to save the partscar and use it as an example car til the restoration is complete.. Have two such example cars and know several other hardcore Pontiac restorers that also have example cars that closely date out of same asm plant as their long term project cars.
Moving a picked, what may be a moderately rough, '68-72 2 door Pontiac partscar as a roller, let's say on a trade, it's always wise to thoroughly carefully clean the door, quarter, and rear window glass and examine for scratches. Usually, the only original glass I'll pull out of such a Pontiac 2 door roller, is the rear glass. Rear glass that isn't scratched is tough to find, and the reproduction back glass avail has its share of distortion, is expensive, and really doesn't cut it in a high level restoration. Am also a stickler for condition of original interior plastic, hard to beat like new original interior plastic. Similar deal with firewall pads, the repro's, even the more correct one are not correct for a very high point restoration, have to source flawless used.
Hope this helps.