I really don't think there is any difference. Ford numbers the cylinders like this:
(looking down on the top of the engine installed in the car)
front (water pump goes here)
5 1
6 2
7 3
8 4
rear (flywheel goes here)
The two firing orders are:
1-5-4-2-6-3-7-8 (289/early 302)
1-3-7-2-6-5-4-8 (351/later 302)
Now look what happens if we number the cylinders differently:
front
8 4
7 3
6 2
5 1
rear
1-3-7-2-6-5-4-8 on the original engine is 4-2-6-3-7-8-1-5 on this engine. Move the numbers around so that 1 is first and you get 1-5-4-2-6-3-7-8
One firing order is just a mirror image of the other.
Exhaust crossover should not be any different. The two middle cylinders on each side of the engine are crossed over. This means that with either firing order, cylinders 1, 4, 6, and 7 feed one collector and 2, 3, 5, and 8 feed the other. This is so that you get an even series of exhaust pulses in each header. Looking at the two firing orders again and taking every other cylinder, we get:
1-4-6-7 & 5-2-3-8 for the 289 firing order
1-7-6-4 & 3-2-5-8 for the 351 firing order
Same set of cylinders no matter which firing order you use, and the two sets match the lists above (which I listed in increasing numerical order).