I couldn't find anything in my usual haunts. But, if I understand, you're concerned that after asembly the supers won't be rectangular?
What I do is fasten a couple of 2 foot lengths of 1x2 at 90 degrees on a work surface. After gluing and nailing 2 sides together, I press them into the 2 pieces of 1x2, making sure each side is against a 1x2. The next 2 sides are nested against the first assembly and on and on...
When I assemble the halves together to make a super, I do the same thing. I use the 1x2's to verify the super is square and adjust if necessary. Then I put the super aside to dry.
What are you trying to do Brooklyn? I can't really tell from your question.
I do use a nailing/glueing jig for assembling boxes but it is really little more than an old box with a few bits of plywood screwed to it to keep the sides stationary for the initial application of the glue and the first couple of nails. an inner cover (a square bit of plywood would also work) with a couple of scrap bit of wood attached and time (for the glue to dry) is all I use to square the boxes.
Some where I have a picture of a box joint sled I use to cut the joints in my 10 frame boxes. Funny how you can't find stuff when you want it. You can goggle box joint jig to find one that will work for you.
To keep the hives square I have 6x6 sq blocks I clamp in the top corner that keeps them square, wellmaybe square isn'tthe right word more like true 90 corners.
As for the size set two frames side by side and measure them. Subtract that mesurement from the size for a 10 frame hive.
It is a shaft drive craftsman from the late 70's or early 80's and was my mothers. Ihave her band saw and jig saw too.
she made all kinds of whiragigs and other gardeen wooden stuff she sold from the house and fairs and such.
several of us appear to be using the same (and yes ancient) table saw. I acquired mine out at the dump.. the table and all was in excellent shape but the motor was toast. since that time I have burned up two motors myself. I certainly enjoy stuff that has multiple lives.... likely a black cat thingee.
19 3/4 long
I though this was suppose to be more like 19 7/8 inches long??? a bit too wide and the frames will fall from the rabbet and a bit too short and either the frames are likely not to fit or bee space is compromised between the end bars and front and back of the box. of course either + or - the bees will not mind much but slight irregularities here can make future manipulation (frame removal) tedious.