P.S. Here are some additional notes, related to the discussion, but not specifically intended for @cynrich
As a general rule, I have observed that:
* Worm-drive circular saws are always left blade. I am aware of only one exception: a Porter-Cable trim saw.
* Corded circular saws are usually right blade, but you can find them in both sides.
* Cordless circular saws are usually left blade, but you can find them in both sides.
Some accessories are specific to either a left-blade saw or a right-blade saw. I saw a plastic crosscut guide at the store that caught my fancy. I was about to buy it until I realized that it is made only for a right-blade saw:
(If you think about it, the mirror image jig for a left-blade saw would require you to hold the guide with your right hand and operate the saw with your left hand, which might be awkward for some people. If you make it to work the opposite way - holding the guide with the left hand and operating a left-blade saw with the right hand - then the support edge would be narrow and it would be good only for a specific blade kerf width.)
I don't have a dedicated jig. I just grab any old board with a straight edge, clamp it to measure, and use it as a guide. I know my saw baseplate (and blade kerf) measurements by heart. Jigs like the one cynrich wants to build are better, because they make alignment fast and easy, and they reduce tearout. I know that, but then you have to find a place to store it, and they are big.
I am right-handed. I have used both left blade and right blade circular saws (and worm drive Skilsaws, too). I prefer left blade circular saws because it is easier to watch the cut as it progresses. I know others who prefer right-blade saws. It is an individual preference.
Not all of my circular saw cuts happen on the "inside" edge of the blade. Sometimes it is easier to line up the cut for the outside edge, and I must take the blade kerf (blade width) into account as I clamp the guide board to line up the cut.
Just sayin'. I hope this extra info helps someone.