M-19216-D46 is the FRPP number for a 4.6. The only difference between it and a 5.4 is that it's a 6 rib pulley and the 5.4 is an 8 rib. Ask Steve at Tousley Ford and he should be able to get the correct one for you.
I would PM the Ford Parts SV and have them look up a regular F150 without A/C (fleet work truck) and with a 5.4L(or 4.6L) to see if there is any pulley or tensioner would take the place of the compressor for the belt. If nothing is needed and it is an empty space, ask them which belt length is need.