Pulling the spark plugs and having a look in the cylinder is a good idea. As stated by others, a stuck valve can cause some resistance, as can junk in the clutch pulley. It won't hurt anything to shoot a little lube in the cylinder, if it's relatively clean inside. Try rolling it over with the plugs out, pull the clutch cover off and see if you can detect if something is dragging in the clutch. Take the valve cover off and look at the valvetrain to make sure it is moving freely. I wouldn't be to forceful until you know what is causing the problem. An Operaters Manual and Parts Book will be very helpful to you. If you are interested, I can roughly estimate when your tractor was built from the serial number and a little math, and tell you whether it is truly a 45 or 46 model. I'm guessing from what you said that it is between 555334 and 558817. I gather info on letter series tractors, in particular model "A". No pressure, and e-mail is open if you prefer.
Welcome to the forum and JD. Hope you get it going without too much cost or trouble..........especially the cost part.