If it's a gasser, cylinder # 1 is on the passenger side front, #2 is right behind it, all the way back to #4 on a V8, or #5 on the V10.

For the V8 #5 is the front driver's side, going back to #8.

For the V10, #6 is the front driver's side, going back to #10.

For instance, for a V8, looking from the front of the truck,

4-8
3-7
2-6
1-5

Or V10:

5-10
4-9
3-8
2-7
1-6

V10 firing order is 1-6-5-10-2-7-3-8-4-9 - no idea what the V8 is