I’ve done a bit of reasearch on English axle Escort half shafts, and they’re not all the same! Appears to be different part numbers for different models, but differences could be due to the flange and brake size fitted.... Reading through various forum threads on the topic finds the occasional poster stating that RS2000 shafts were thicker, but without any evidence to substantiate. Certainly Mk2 RS2000 shafts were different to Mk1, the flange centre being altered.
Gp1 halfshafts are the ultimate answer, but at an ultimate price....