ACT English Question Help?

Test Preparation ACT Preparation
1

This is from the 0359F ACT English Section (2005-2006).

Question:
The quill of this replacement feather is trimmed so that
when the replacement feather is eventually attached to the
quill stub still in the bird’s body, the repaired feather will
(BE EQUAL IN LENGTH) to the original, whole feather.

Answer choices:
70.
F. NO CHANGE <- Correct answer.
G. be equally long <- My answer.
H. equal the length
J. equal in length

I’ve been pondering about the difference between “be equal in length” vs "be equally long.’ I don’t understand why the correct answer is correct.

2

Solved here: http://blog.prepscholar.com/adjectives-vs-adverbs-for-act-english-grammar-rule

3

“repaired feather will be equally long to the original” sounds strange. The “to” after the underlined part kind of ruins that choice.