I have a 22.5 1020 on a'98 2344 with the pump (fuel) turned up 1_2 of a turn and it has no problem in any kind of beans up to 4 mph in a smooth field.I usually average about 3.2 as in rougher fields the head and combine won't react fast enough.I am also one that believes in get a bigger header and goe slower theory as going slower lets the heads perform properly and slower is easier on the whole machine.It would handle a 25' in beans or when cutting wheat just for the grain. The only time it starts to lug down is when a farmer(customer) wants all the straw I can get,so I have to slow down to 2 mph depending on how tall or thick the wheat is.Running the head locked up in manual(tracker and flex) in uneven fields,not to mention the odd stone,getting all the wheat straw requires a slow speed anyway. My 2344 turned up 1_2 turn is probably close to your cummins equiped 1660 but not more so ya I know it would work.Go for it! P.S. You will also use less Gal_acre which is important considering where the price of diesel will go! It makes me wonder about some people that run 6-rows+20'heads on 77-88 an even later year 66 series machines if they have a oil well in the back forty!