[DeTomaso] Aldan shocks help!

[panteratime at aol.com]

Folks,
The guy at Aldan wasnt sure if I should get their 658HP or 655HP shock--Wants me to measure original shock on car.  This is for a rebound adjustable shock with poly bushings $400 a set.  Any suggestions on which one I should get?  I understand ride height is the difference.  My car is stock 1972 with original front shocks, not a race car!. 
Thanks in advance for your advice.