I seem to recall that the smaller Garami sport biplane is almost a Bostonian, though I won't guarantee it:
Not sure what the 7 gram rules say about biplanes. You'd have to get rid of some of the sheet wood, I think, and shorten the top wing. Maybe widen the fuselage a tad.
Other than shrinking it, I don't think you'd have to massage Keith Laumer's famous Twin Lizzie very much to turn it into an attractive Bostonian:
Maybe John Oldencamp's Silver Schtick design is simple enough to get down to 7 grams:
There are a few other Bostonians there, but not sure they're simple enough to get that light.
Apparently, it's possible to make a scalish Bostonian that only weighs 7 grams. At least, if your name is Jack McGillivary. I have the 1987 thru 1989 edition of Winning Indoor Designs. His winning Bostonian was patterned after the Pilatus PC-6 and the color scheme (!) is from the second airplane on this page:
The nose on the model is smaller and shorter, though. The airfoil isn't scale at all, very thin with concave lower surface. If that tickles your fancy, I could scan the page and send it to you.
If that's possible, I wonder if anyone could adapt Walt Mooney's attractive "Old Howard" bostonian to 7 grams.
There are some other Bostonians in the Mooney collection on Hip Pocket:
This one doesn't show up in a search on "Bostonian", so recommend you also search on "Boston":
There is a Bostonian called the DeHalibut Bosty Moth which was in Model Builder. If you like it, I could send you the plan. I feel funny posting it on the site, because it isn't that old. See the picture attached to this message.
I've collected some others people have come up with:
-The Flohp, based on the Floh (!) biplane! (probably not good for high times or low weights!) The plan claims it's very close to scale except with a narrower chord.
-Gee Whiz based on the big fat Gee Bee
-Stagger Wink Not sure if this one is legal or just Bostonian sized, as the plans say.
-Mass General Based on General Aristocrat. Rather attractive. I think it is also on Hip Pocket or Outerzone, so check there first.
-Another one based on the turbo version of the Porter.
-Fat Cat based on Nesmith Cougar