I can offer the same opinion I offered on FPN, but I'd like to hear David Isaacson's take on this one.
Rough week. I'm already getting chewed out here as someone who doesn't like people who don't live in gated communities (???) because I've been bit swamped this week/month/season and am slow to answer emails
I'll play with this more in detail I hope next week, but briefly, 10-feather nibs are found, always (so far) monotone. They fit Maximas (and perhaps could be further arched along long axist to fit Sl Max. Collector Convention holds that these were late Parker replacement nibs for Duofold Senior. We don't object though (save for the minor value issue finding monotone nib in those pens we'd expect to have two tone) to finding them in Vacs.
As to mixes...
Slender Max after late 1939 has same contour as Major. Diff being cap-band, Section inner-diameter (to hold feed), bigger feed and nib. Often opposite mix is found, a Slender Maxima cap-barrel with Major nib. Finding the reverse (potential reverse, keeping open mind) of a Major cap-barrel (barrel proper of course the same after late 1938), with Sl-Max nib is no value loss indeed a value gain, even *if* nib/feed/section is bit of swamp, as Slender max front ends are not easy to find
regards
d