Sorry, my first response missed your desire to use a stock circular saw. But I suggest you not go there. I used another rail system for many years that required a base be bolted to the saw and I didn't know what I was missing until I bought a dedicated track saw system.
Also, for years I avoided a plunge saw because the first time I used one I didn't like it at all. After using my plunge saw for a while I love this design for the rail. Standard saws make you hit the rail hard enough to bump the blade guard up. Or if the saw is already on the rail the blade is totally exposed.
Ha - I'm a tool collector/user and another alternative is to use the saws below. They are designed to work on a track but are designed like common circ saws. I purchased the 7-14" one only to find out a year later they released the 9-1/4" so I have both. The 9-1/4" does incorporate a thumb lever to aid opening the blade guard when used on the rail. This 9-1/4" is the cats meow for deep cuts on the rail.
https://www.toolnut.com/makita-xsh0...P1IhIkQACqm_oB_3K0MyGOttzB0XPtmRoCpa0QAvD_BwE
https://www.toolnut.com/makita-xsh1...ss-cordless-9-1-4-circular-saw-tool-only.html