yep, though really easy, you just need a bucket, a socket set/torque wrench and a measuring jug and a vice with either soft jaws or some cardboard to protect the fork , the manual for marzocchi 48s is on the sight somewhere, the gas gas manual has spring change info but its for the open chamber 45/48s.
it wouldn't take you an hour including removing/replacing forks from bike.if you need help let me know.
I'll go measure, I know the Sachs 48 were kyb 48 so I'm thinking they'll all cross over, the replacement springs I bought for the Sachs were longer like you've noted from memory, the marz48 stock were 5mm longer than the replacements I got from two wheels. The Sachs stuff fits in Marz 50, and Showa 49/47 as well, i Think. Varing lengths of course.