When changing to 5 speed, two things to know are the gearbox mount is further back and the speedo cable exit is further back as well.
RHE will have made provision for fitting a 5 speed, on my S7 there are two cutouts which can be removed, I braced across the front of the 5speed cutout to reinforce the gap left where the 4speed mount was.
With the speedo cable get hold of a 5speed cable which is longer incase the current one doesnt reach it did on my S7.
goodluck
Jez