Hb. 4:3: It's meaning and translation

At Hb. 4:3, 5 Paul (if he wrote Hebrews) is now arguing that those who believe will enter the rest, using Ps. 95:11 as his basis, the same passage he used to warn those who may not enter the rest at Hb. 3:11.

The KJV interestingly translates these same Greek words differently. At Hb. 3:11 it translates them, "They shall not enter into my rest," but at Hb. 4:3, 5 it translates the same Greek words as "If they shall enter into my rest." I am under the impression that the Greek may actually be translated as either, but I don't know many modern versions that actually try to manipulate the passage as the KJV does to go along with the author's argument.

An ancient manuscript (P13) actually omits a word at both Hb. 4:3 and 4:5 to make it read perfectly with the author's argument, "They shall enter into my rest." Codex Alexandrinus does the same thing at 4:3, and Codex Bezae and a few others do it at 4:5, but all of these almost certainly represent scribal manipulations to make the text fit more easily with the author's argument.

Any other versions translate Hb. 4:3, 5 as the KJV? What is the best way to translate and understand this passage?

Yours,

Bluefalcon