I'll guess late 1951 to early 52. 52 was the last year of the round shrouds. With all the tractors I've got and others I've seen that should be close. The best way is to get the numbers off the engine to date it as Bruce said. If the tag is gone take the flywheel off and there will be a 2 digit casting on the back. That would be the year the flywheel was casted.