Rotators:
https://www.stovebolt.com/ubbthread...valve-rotators-need-advise-see-pics.html

Rear mounts:
The mounts go between the bell housing and frame crossmember. The design of the crossmember changed in 1954. For example, to put a 1954 235 engine in 1949 frame, use the 1949 bell housing and 1949 mounts.

Clutch questions (did you look here?):
https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1278237/all/clutch-info-needed.html

Starters:
Both. Used outright. Rebuilt (rebuilding service), you pay core price and get get deposit back when old one sent in. Most rebuilt sales will specify core charge if one is required.

Oil filter:
Hard to believe but an oil filter was optional.

Tag with 140 PSI:
Maybe a cylinder compression test was performed. Results were 140 PSI or higher on all cylinders.

In the order of importance, what I follow to identify a 261 engine.

Captain's bars
Block casting number
Block date code
Block serial number (near distributor)
Head casting number
Head casting date
Engine color
(record results, pencil in your owners/shop manual)

With debate on engine colors:
1954 green
1955 green some may be yellow (mine was green)
1956 yellow
1957 yellow
1958 to 1963 green

Orange is the V8 color but is also the most common spray paint used by Chevrolet engine rebuilders. Looks better than rust.
When it came to 261 engines used in working or commercial big trucks, parts are parts as long as they are interchangeable.
Appearance is less important. Whatever it takes to get the big truck back in service.

Last edited by buoymaker; 06/09/2022 4:18 PM.
"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."