Optimized adult size Frijole
I'm 6ft 4. I say supersize it and make the seated height a good 20 inches! Now that you have established a frame that is very comfortable, and have optimized the handle bar dimensions and ergonomics that makes it ride and handle beautifully, then you have the beginnings of a really good bike. But to make it great, and maybe even better than the real Frijole, you must also make it very aesthetically pleasing. The styling is what makes people love the look of the Frijole. In many ways, it is about keeping it simple and using pleasing radiuses and shapes that work well together. Hit those elements of style like the Frijole exhibits and you will have a winner. I personally like my frames a little taller and perhaps there's a way you can make two sizes just by mounting the axle mounts under the frame tubing on the large size and use front forks one or two inches longer....
Your latest roller frame looks really nice, especially with the Astro's and the universal Trials tread tires, 530 x 450 x 6 tires if I'm not mistaken. But I'd say there are some spots on the frame where the shape of the radius could be tweeaked. The radius of the tubing that passes over the rear tire to the axle ends is not quite right to my eye like the original Frijole is. It really needs to match the curvature of the tires. But, of course, this is likely to be hidden by the cylindrical tank behind the seat which is a must have for style. I like your front forks a lot and the forward kick in the handlebars, especially if they make the bike handle really good and are at a comfortable height and distance forward for an adult.
I think the seat your using right now is not doing the frame any justice. One of the key style points of the original Frijole is the simple oval seat with no kick up. The seat you're using just doesn't do it for me. But, the great part about seats is that they are easy to change based on personal taste.
The frame needs to be able to handle at least the height and dimensions of a Briggs 5 flathead and maybe more HP. It appears that yours does this easily. So now if you can build this frame, possibly with an optional front fork that has a simple suspension, and maybe see if a swingarm could be put on the rear with spring suspension incorporated into the two rear downtubes, then you'd have a fully optimized RestoMod Frijole Clone in various sizes for Adult riders. I think the orders will continue. I think that if you are able to adjust dimensions for customers, people will commission these custom frames. Then we'll see even more really cool bikes like these pictures that inspire me....not mine...