Nice work Cap'n
To avoid stripping a thread in the future, turn the cam as you put on and tighten down each rocker arm.
You should be able to put each rocker arm on so that no pressure is on the cam lobe and arm, which causes the uneven tightening down of the 4 bolts and very likely strip as you encountered.
I almost stripped one of mine as well until a machine shop guy told me that trick. I think at TDC though, only 2 and 3 are under some pressure.
'91 300E, 211K miles