I believe the first year they had a greywater tank was 1974. It's not a big enough tank to really be excited about, but it'll come already plumbed for greywater storage at least. I've managed to put up with the 12ish gallons of greywater tank in our '75 24' Argosy for several years, but in the 28' renovation I'm at least doubling that. '75 and earlier had all flat hinged doors for lockers except for the ones built into the interior endcaps, which have plastic tambour doors. '76 and later went to tambour for the overhead and under-furniture lockers, with all the issues of tambour doors. I prefer the hinged ones.
EDIT: Oh, and between 24' and 26', the 26' has some nice advantages. It has a significantly bigger bathroom, not big enough to be wasteful of space but big enough to sit on the toilet with the door closed without having one foot in the shower. I really, really like our 24', the first RV I've ever owned, but it did teach me a few things I want in the next one, which I'm working to implement in the 28' reno.
The 24 was a good deal in great shape, and I initially liked that it has a dinette. The dinette is very nice when we're sitting down to eat, and somewhat in the way the rest of the day. If we have guests on a rainy or hot day (when we want to be inside) the only places to sit are the dinette or on the beds, and the beds are too far away to be part of the conversation at the dinette. I looked specifically for a trailer with a front gaucho when I was looking for the project trailer, with the flexible folding table that can be half-open for holding drinks/snacks/computer/etc., or fold all the way out for a meal, or completely out of the way if needed.
Il Carriaggio — 1975 Argosy 24 | Il Progetto — 1976 Argosy 28 Center Bath | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill