Actually, they both are right.
Having owned "a few, and still do", and worked on Perazzis since they became popular in this country, the Perazzis are almost all "trigger plate actions" in that the hammers and sears are attached to the trigger plate. Perazzi became famous for competition O/U shotguns, trap, skeet and Bunker. One of their claims to fame was the removable (drop out?) trigger assembly. Perazzi also built the same basic design model that had a non-removable trigger group, and utilized coil hammer springs.
The early hammer springs were somewhat prone to breakage, so they needed to be taken out to be replaced, and you could do it yourself on a trap field. The coil springs eliminated this requirement, but the removable trigger group is still used, with a choice of coil or leaf springs on many models. The current hammer leaf springs are a lot more reliable than the early ones, so maybe you don't need to take it out to replace a spring, but it is nice to take the trigger out to clean and lube it once in a while.
And a lot of people feel the leaf spring guns had a faster lock time. In the early days (late 60s, 70's) some gunsmiths converted the leaf spring triggers to coil springs, Pachmayr was one, probably others also.
Perazzi early on built true side lock guns, O/U and SxS, which are pretty rare and pricey. Perazzis were all box lock guns, save the sidelock guns mentioned, and are "trigger plate actions" as hammers and sears are mounted on the trigger plate. I am not sure about their current side by side as I have never looked inside. I believe it also has a removable trigger assembly.
Early on, Perazzi even made a removable double trigger assembly for the MX8; now that is a rare bird today.
As I remember, their MX8 model O/U was named for the Montreal olympics in 1968, which they won, wish I could remember the shooter's name, someone will, no doubt.
