Working out how long coil over shock springs should be.

[mrcrappy]

Hi guys, I am thinking of buying some replacement front coil over shocks for my TVR 350i, this currently has the cortina type set up with massive diameter springs, Spax do a direct replacement coil over unit (G2011) but have no idea what length the springs shoud be, has anyone got a clue how to work this out? is it as simple as adjusting the spring seat halfway up, open the shock to full length then measure between the spring seat and the top spring retainer?
Any help would be most appreciated.
All the best
Jon

[mrcrappy]

Thanks thats a big help, sorry I didnt respond earlier, I didnt realise i had an answer.
All the best
Jon