Gutted 1950 bathroom - removed tile and mortar bed.

Several of the subfloor planks (especiall near the tub) are in bad shape - cracked / huge empty knots / hacked by the original plumber?

I was planning on cutting the dammaged planks half way over the joist. This leaves 3/4" to screw in new plank. Is this enough?

Over the top goes 5/8" exterior plywood, then RPM mat and Ardex.