Hey Rick. I didn't have to mess with swapping camshafts as the head Papa bought was only very slightly used and ready-to-run (like I said previously, great score). Indeed; with your lifters having been disassembled they are now collapsed; there is still valvespring tension pushing up on the camshaft lobes. Assemble as carefully and evenly as you disassembled; even if you have to turn fasteners one quarter turn at a time in sequence (draws the camshaft down into its saddles square).
Even though I've built literally dozens upon dozens of engines (maybe a hundred or more? lost count years ago), I still take advantage of technical info. In Papa's car's case, I went to a local library and checked out a Chilton book on E34s. Even before I turned wrench one on Papa's car, I read and studied the tech manual and 'schooled up' on the specifics and idiosyncrasies of the M50 platform. I then browsed the internet, that's how I wound up here. I'd highly recommend you do similar; having the book in front of you is invaluable if you run into a snag, especially if you're on a late-night thrash and technical questions on this or other forums may not get answered in a timely fashion.
Anyway, I did have to time the camshafts and the motor. On the back of the cams are cast square bosses; to have the cams timed at TDC cyl #1 the intake and exhaust lobes must be pointing tward one another at about 45* up angles. At this alignment, those square bosses on the back of the camshafts will be 'square' to the head, i.e. horizontal to the deck/valvecover surface.
With the motor at TDC #1 (cylinder at the very top of its stroke) the timing chain sprocket is installed on the exhaust cam, followed by the transfer chain & sprockets. This is a very abbreviated; there's much more to it than that. As I said... beg, borrow, or buy a book. You certainly seem to enjoy and appreciate your car or you wouldn't be going through all of this; a $20 book will pay for itself many times over in the years to come
I can do a specific write-up on camshaft timing if you'd like. I'd need to budget some time to do it, so let me know