With a bridle joint, you have one piece that is the mortise and one piece that is the tenon. To create saw guides you need to create 2 for each side of the joint.
I take a piece of 2x4 which I had in my scrap pile, square it up on all 4 sides. The thickness needs to be even but not a specific measurement. The overall saw guide will be 4 inches long and the depth for the guide position will be 2 inches. I will also create a spot for a magnet to make the saw guide easy to use.
Next, I lay out the joints on some test pieces that are sized exactly like the final pieces. Using these layout lines and the measured thickness of the saw I plan to use to cut the actual bridle joint, I make my marking guage match this depth and mark that on the saw guide. I cut it light leaving all of the marking gauge line. I then use my router plane to ease up on the desired position.
I repeat for each guide in the pair. Then I repeat for the other side of the joints pair of guides.
Once I have the saw guides, it's time to test and adjust the fit. As with all saw guides (I have played with many commercial saw guides - aka David Barron), they are simple to use and if layout is done correctly produce amazing results. With these bridle joint guides, I'd say that layout isn't even that big of a hurdle.
I designate a specific face side to both legs and aprons for orientation purposes and clamp the saw guide to that face. I then bring my rip panel saw up and let it do the work to depth. Easy as that.
For the mortise side of the joint, I chop out the middle piece and for the tenon side, i saw the outer pieces off.
I tested the fit. I found it too tight, loose, not even faces, etc. and had to cut the end off and adjust the fit and try again. It took 5 times to get a good fit.
Now with the saw guides, it will be a super simple job of cutting the actual joints and glueing them up. That will be next.