As Simon mentioned,the best way to work out your shock lengths is to cycle your suspension through its full range of motion,this can be difficult in a static state,but is achievable.You then need to measure the distances from your prfered type of mounting point,paying special attention to the closed length required.
You can have very long shocks,but the drawback to most of these is that they have a large closed length,and therefore inhibit UP travel,unless you alter the mounting points.And with the standard L/R suspension setup,you can maximise the available travel on the front with much less extreme length shocks.
I run 3" springs in my 110 and am able to maximise the available travel in the front end, by raising the front turrets 2" and running longer shocks.In the rear I have 3" longer springs and the same shocks as in the front,and modified upper shock mounts.I find this setup allows the vehicle to be very stable offroad whilst allowing all the wheel travel that I require,and I do tend to wheel hard.
I am a believer in having the springs retained F&R to maintain stability,so having huge length shocks on the rear is in my thoughts overkill with the standard Rover A frame and balljoint.But that is just my thought and everyone is entitled to their opinion on the matter,which has been discussed many times before.
If the vehicle is being built with these sort of specs,I am assuming that it is being used as a hardcore weekend wheeler,and not a tourer or fast overland racer.And with that in mind,I find the use of remote reservoir shocks to be overkill,as slow cycling of the shocks,isn't going to get the shocks critically hot enough to reap the benefits of the remote reservoir.
What you will also find is that most of the long remote reservoir shocks are fairly large in diameter and will foul when run inside the front springs on a Rover front end,requiring modification to external mounting,and although not a big mod,it is just another thing that requires modification,for minimal gain.
All of these thoughts are in regards to keeping the vehicle roadworthy,if not being used on the road,it comes down to how deep your pockets are.
