What year 261 engine? The oil filter systems differs for 54-57 and 58-63.
Here are locations of casting codes on a 1960 261 engine (painted the Alpin Green color common to most years that 261s were built.
Here is a good history of the 261 (compliments of Jim Carter). Here is the classic article on Soupin Up a 261 (1955 Hot Rod Magazine). Here is Chevrolet article, introducing the 1954 261.I would not hang any 216/235/261 at the clutch housing on any engine stand - the resultant front-heavy length would scare me. If you do it, be sure you have a 2,000 lb engine stand (for greater stability). Most likely, you are going to have to remove the clutch housing (and most likely the clutch assembly) anyway, if you are going to use this 261 in a pre-54 truck.
Other people will most likely give good advice on how to start an engine that has been sitting. I'd drain and change the oil and replace the oil filter (if you have a 58-63 engine that had an oil filter you MUST have the oil filter system in place (you have a full-flow oil filter). Post a picture of your oil filter and we can identify it (the year of your engine will identify it, also). I'd put in all new ignition parts (points, plug, condenser, distributor cap, rotor, and ignition (plug) wires).
I'd suirt something like WD-40 down the spark plug holes and let is soak 24-hrs. Then I'd try to rotate the engine.
Other people will (hopefully) post suggestions regarding the carburetor and fuel delivery for a start-up test.
