How do I find the correct shock for the rear with modifications? 68 Barracuda

My 68 Barracuda has super stock springs and a lowering block was used to get the right ride height. The center to center measurement on the mounting bolts is 21" in the normal ride height. The replacement shock chart shows 14.125 collapsed and 23.375 extended length. Is this enough travel ? Or is there a way to find out what shock I need ?

Maybe a little more back story would help? I just bought this car and it has/had Competition Engineering "DRAG RACE ONLY" shocks which are clearly marked as such. I removed them and when I compressed them they don't move, zilch, nada. I assume they're junk ? Either way this is a street car NOT a drag car. I want to make sure the shock will be in the correct extended AND compressed range so I get the best ride quality. It seems to me that the 21" normal ride height would require a little additional extended length ? The previous owner put the super stock springs on it but they lifted the back end up too high , so he added blocks between the axle and the shock mount (you can see them in the picture posted) I really like the stance and don't want to change the set up I also don't want to guess on the proper shock. Thanks for all of your help with this.

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old chrysler imperial shocks , with the eyes changed , " if need be "
I bought mine at o`rilies or summit years ago , but took them back off for a caltrac set up ...