Homebrewing: Hop Schedules

I'm making a pale ale this weekend, and the instructions have these hop additions:
1.5 oz Simcoe at 60
0.5 oz Simcoe at 15
1 oz Cascade at 5
no dry hopping

I ordered a couple extra ounces for dry hopping. My question is whether or not it is neccesary to have a 5 minute hop addition if you are going to dry hop. Since the 5 minute addition is for aroma, wouldn't you get plenty of that with the dry hopping?

Only reason I ask is because I have 4 ounces of Simcoe and 2 oz of Cascade. I intend to use 2 oz of Simcoe for dry hopping. I would like to avoid using Cascade at all.

using brewer's friend, the recipe as written calculates 75.51 IBUs. Cutting the 1 oz Cascade at 5 minutes lowers it to 71.04.

My other option would be switch to a 0.5 oz Simcoe at 5 minutes, then dry hop with the remaining 1.5 oz. This brings the IBUs 75.01.

right now, my lean is towards the last option, all Simcoe with 0.5 @ 5 minutes and dry hopping with 1.5 for 10 days or so in the secondary

eta:
just realized that the intended IBUs for this recipe is 53, because they call for a partial boil and I've been calculating with a full 5 gallon boil. I can get much closer by going with 1 oz at 60 instead of 1.5

Clone recipies for Russian River Row 2 Hill 56 seem to land somewhere in the 40-45 IBU range. After further review, I believe I will go with this:
0.5 oz Simcoe at 60 min
0.5 oz Simcoe at 25 min
1 oz Simcoe at 5 min
2 oz Simcoe dry hop in secondary for 10 days

calculates to 42.5 IBU