What most people use (and Pantera vendors sell) are the Proma Stars, single adjustable model # DR5855B with a bearing end (rod end) or equivalent poly bushed model is DR5855P. If you want to go double adjustable the part #'s
are DDR5855B/P. These shocks take a 12" spring and extended length is 17", compressed 11 5/8" close to oem shock specs.
My GT5 is set to ride as low as I can go (rubber touches the flares on occasion) and the spring perches are maybe an inch from the bottom, so as David suggests you can probbaly go down to the next shock a DR4955B (or DDR4955B for double adjustable) which is 15" extended and still 11 5/8" compressed, but uses a 10" spring and then have it further up the perch to achieve ride height.
More info here; QA1 Proma Star
I noted recently that both Jegs and Summit have dropped the 'B' versions, but they still show on QA1's catalog. They require mount spacers as the mounts are considerably narrower than a stock shock mount. I can supply a drawing of what's required (and what the Pantera vendors supply) or you can choose to slightly modify the mounts as I posted on the e-mail list;
The difference between the rod end internal diameter (0.5" dia.) and the bolt (19mm head = M12) is 0.7mm (0.02") so to save yourself a bunch of work machining spacers you can choose to drill out the metric shock towers on the Pantera body and a-arm mounts to 0.5" (currently 0.471" imperial equivalent) and source an imperial bolt with 0.5" shaft. Then all you will need is a length of tubing of 0.5" internal diameter and 0.1" wall thickness to cut into 0.6" lengths as spacers each side of the shock rod end. You'll need 16 of them to complete the job.
Julian