plunger spring cap recess

Is your slide's mainspring plunger cap recess clean through the slide or is there a ridge near the dust cover end to keep it captive?

What is spec? 

Having the captive ridge makes installing and removing a full length guide rod very much harder.  Is a flgr worth the hardship of altering my slide or should I just keep the gi setup?

I believe you are talking about the recoil spring plug tunnel on the slide. Older GI type slides and Colt have them. Newer pistols in many cases do not have the ridge. I do not typically like flgr. 
Jon