The cheap sornheads you will find will have an orange frame, tehse are ok but a bit harder to work on, older as well. They progressed into the black frame series from there, I have an A 240 head on my K2, these are somewhat of an updated model from the orange ones. The last Allis Chalmers heads to my knowledge are the three stripe ones, they are black frame and have Allis-Chalmers and three stripes on each outer side of the galvanized part, these are worth more yet. If you get a greenstripe head, it will say Deutz-Allis and means it is of 86-87 vintage, worth more yet. Hope this makes sense and helps.