Ransomes Auto Certes 18in mk7a cutting cylinder replacement

Folks, I have recently joined the club and would appreciate a bit of a steer with how best to tackle the replacement of the cutting cylinder on my trusty Ransomes Auto Certes 18 MK7A. I am reasonably handy and tooled up but not sure if there are any tips on do's and don'ts before I start at it like a bull in a china shop.

I have a new Cylinder and bottom blade from Garfits.

Is it easier to take off the engine before starting this? Is it reasonably straight forward to do? Any special tools required?

Any steer you could provide would be gratefully received. 

Ferg