allis D-17 series

I have a 57 D-15 which I like for many reasons. It is a bit light HP wise to handle everything I need to do on our acreage. I'm considering a D-17 either diesel or gas. The early D-15's don't have what I describe as live hydraulics which makes loader work difficult. Some where I recall reading that Allis improved the hydraulics on the D Series to provide constant pressure whether the clutch was engaged or disengaged. 

Thanks Gary. I see on tractor Data that production of the D-17 series IV began in 1964 w SN 75001.  Were there any additional improvements made in the later years 1966 thru 1967 that one would want?

My recommendation would be to look for a D-17 Series 4 with a gasoline engine. Engine parts for the D-17 diesel are hard to find and expensive.