Robert, the D19 was produced from 1961 to 1964 and was rated at 71 PTO hp (gas) and 67 PTO hp (diesel). The D19 is a good tractor, except that the gas version will use its weight in fuel (plus some)! We have a 1964 D19 turbo diesel that was used this week in mowing hay (7' Vicon disc mower). Relatively easy on fuel. Inspect the diesel models closely before buying, as some were known to have engine problems (cracked heads, headgasket). In central Missouri, a D19 will range from $2000 for a fair gas model, to over $4000 for a late diesel model with 3-pt hitch. Overall, they're alot of tractor for their price.
If you're new to A-C or want more information on the D19, I would recommend Norm Swinford's book "Allis-Chalmers Farm Equipment 1914-1985" and C.H. Wendel's book "The Allis-Chalmers Story".
Enjoy your D19!