Hi guys when I get to my stage in my build that I get the rear done(diff,coilovers,4 link etc etc)I want them to brace it as well to one bar in the cabin behind the seats.I also wont a harness bar as I put up the question ages ago about bolting them to the floor,which everyone said is no good due to spinal compression.Is this technicaly a roll cage?

Any info would be great.

No it's not a roll cage only really a taxi bar which is meant for harness"s.but what are you meant from the question?

If I understand this correctly you want a single bar horizontal that will brace the shock/spring mounting locations. Couple of things here; first a harness bar should be as close to the seat as possible the longer the belts the more they will stretch, the shock mounting point is probably 24 inches from the back of the seat and the belts may stretch enough that your head could hit the steering wheel if you ever had a big impact.
If you're willing to have a 2 seater then just put in a proper rear hoop with the diagonals that will stiffen up the chassis and allow for properly mounted bets

Tom