Just an update... Apparently the older Zacconi machines were 45mm, but this on is 49mm and actually measure 49.9mm about half way down the basket. The cherry tamper that the previous owner made is about 48mm, and it clearly too small when I use it, so I'm going to order a new tamper, probably 49.5mm, from Orphan. I'm also going to see if they have a bottomless PF for it.
Thanks... I was just looking at that. Ouch! I'll probably still order it Did you measure your basket? This on measure 49.9, so I'm think the 49.5 would fit, but maybe I'll go with a 49.4 just to be same. What a mm between friends :-D