Check the orifice size, as that is is used to tune the assistance given by the PAS system - smaller =heavier, if it wasn't obvious, as it is a flow restriction.
The P38 style pump is the same.
Double-roller chain, Turner will be able to advise.
Check the rocker shafts for wear on the under side, or you are wasting your money with a higher lift cam.
I run an H200 with Rhoads lifters which allow you to get away with an auto -sings at higher revs
Honestly the only reason people used twin shocks in the past was because older shock tech was just not as good as it is today.
Single will be more than you need unless you suddenly need to go and do Baja.
FWIW I have see 110 hi cap tub fitted to a disco without shorting things and recking it looks loads better than a series/defender standard tub against the disco bodywork.