It is my feeling that if someone can do a brake job - including calipers/rotors on the W123 then they are competent enough to do the cyl hd R&R. Did you do the timing chain guides at the bottom of the engine area too?
When I first ran the 240D after the rebuild I kept driving around a 5 mile perimeter from the house for the first 25 miles. Just try to carry a cell phone with you
Once I get the 240D where I want it I am probably going to pull the head on the 300D to see what I have. My plans were to get to 250k before doing it but it is based on when I take the 240D down off of the jackstands - doing brake hoses (at the calipers) and front wheel bearings this week.