If you have trouble still after following the MM suggestions, put a heavy prop on it. Something plastic, and bigger than you really want to run. It will give you enough inertia to make starting easier. After you get your settings into the ball park, you can switch to a realistic flight prop.
If, when you flip, you find it gets stuck at TDC or doesn't rotate thru, you likely have one of several issues:
--the engine is dry. Give it an exhaust port prime, but don't hydro-lock the thing and bend the rod or wrist pin--or break off your finger!
--the contrapiston is backed way out. Usually, the bottom of the contrapiston should be near-flush with the inside of the head as a good starting point. On an engine that you just received, you will have no idea where the contrapiston is, unless you buy it from a diesel guy that you trust. And, once you get it set, you rarely move it much--only backing it out for cold starts, or if you change prop size.
--the engine has lost its compression seal. Look at the piston and check for scuffing and scarring. It should be shiny near the top and brown down the rest of the way. If it has been cleaned, it might not have any varnish on it and that can make it harder to start. If it was improperly cleaned you can lose the fit, and therefore the compression. And it will be hard to start.
--the prop inertia is too low to allow easy starting with any combination of the above problems
Remember, when running diesels, take your shirt and pants off on the back porch before you come into the house. And, when you want to get the diesel stains out of your clothes, you use scissors.....
Dave