arthr31,
I have a 1601D too, and there are similarities, but there are some big differences as well. Externally mounted filters for one, the throttle position mentioned earlier, the ROPS of course, and now as Norm said the plug that indicates a two speed PTO selector.
The price now is: $4200 with out the finish mower. And I should have more numbers....valve cover id, etc. That might help....so would a picture of what's under the hood.
Mark