For a DT466, I believe you will need a 600 series Allison due to the fact that the DT makes at least 210 hp in stock form, like the 1160/3208 CATs and 6-71 Detroits that also run the 600 series.
If you are going to use a slightly less powerful engine like the 8.2 liter Detroit (around 170-190 hp) or a DT360, I believe they would mate up to the smaller Allison, the 545.
If you have any questions that you can't answer just call. I do this stuff all day long, all week, all month, all year, etc.
Patrick
(559) 251-3814
WheelchairBusProject@yahoo.com