Front driveshafts, 3 questions.

Background is I'm restoring my '91 sapphire (I've owned it since it was 2 years old) and it's a bit of a "Triggers broom" as it was re-shelled by Ford just before I bought it (in '93) and lots of the parts don't match the year.

1 - Ford7zap say the drive shafts should be 1634970 both sides pre-Jan 90 but should be 6478335 (Right hand) and 6672254 (Left hand) after. What is the difference ? It seems the inner joint is different on my RHS compared to LHS. The LHS needs dismantling like a normal CV joint (twist it to an extreme angle to get the needle bearings out, one at a time) but the RHS just falls apart.

2 - Is the circlip inside the front diff actually required for the RHS ? When I asked Quaife about upgrading to their ATB, they said no clips either side, just rely on the springs in the inner joint...

3 - What is the supposed drive shaft length issue ? Mine will NOT be lowered, I've already replaced the springs with uprated - but standard height ones - (try driving in rural Suffolk/Norfolk and you will know why) but I read lots about the standard shafts being too short ?? Especially of interest if I'm going to leave the circlip inside the diff off the RHS shaft.

I hope that all makes sense.