You should be able to turn the engine over several revolutions with a bar. The problem more than likely is not with the flywheel. Check the oil and look for signs of contamination, too much oil, gasoline, coolant. Remove the spark plugs and see how it turns over with a bar and the starter. See if it has any coolant or gas comming out of the plug holes. Check the plugs to see what they look like. You could have a head gasket leak which would fill up some cylinders.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine