You may have owned a Beretta 391, but I doubt that you owned a Benelli 391. As far as drop at comb goes, I wouldn't generalize by saying that straight stocks won't fit you comfortably, because a straight English type stock can have the same drop at comb as a semi auto , or an O/U shotgun.
I need a low drop @ the heel to fit me . About 3 " is right. Most new guns are about 2 1/4" & I shoot high with these ones.
I collect & shoot old S X S doubles , of which many have the 3" drop. I have lovely AYA Model 25 BL , made in 1978 , with full
engraved receiver , 20 ga.. Drop is too little & I gave up finding a stock maker who could make a stock for less that the total gun
is worth . I love this gun but can not shoot it well .
So I sympathize with you ,,,,,,,,,,,, The guns you want don't fit . ,,,,,,,,, Frank