And just a little addendum, the Maintenance manuals for thr T28A are also the same for T28D with Supplements for armament, Power Plant, Performance ect for the D model. Structural in the main except for spar carry through beef up and 3 hard points on each wing as wellas significant doublers in the centre section, basic Electrics and Hydraulics are same.
The Undercarraige is the same on both aircraft, but the T28D has nose wheel steering. The T28 C has same U/C but the nose wheel is smaller and the propellor is different.
All T28 aircraft have no squat switch because the U/C is manual/hydraulic.
For info the P 51 T 6 also have no squat switch for same reason, I have flown both and the Flight Manual makes a big dealout of the pre start check.
And the pre start list is very short 5 items.