Actually, the first frankenbike I built was full suspension.
https://endless-sphere.com/forums/viewt ... cing+betty
It worked great, and was able to run 35mph down a washboard dirt road with a full load of camping gear aboard. It had minimal welding, which I did with the worst stick welder ever made.
When I got the wire feed welder last winter, my first project was this one. The first compact longtail.
https://endless-sphere.com/forums/viewt ... =6&t=66005
It ran great, but mistakes in the welding resulted in a crooked wheel. I made the rack too high, and most of all, the cheap bike I started with was not a good fit for my body. I just wasn't comfortable riding it really.
But as I built it, and after deciding I hated riding it, I began to think about a compact extracycle attachment. One that would make a good frame you like to ride just 6-10 inches longer. The original extracycle is a great thing, no doubt. But it does make a very long bike!! Not all have the space for one.
After I find the mistakes, you could make this your first project Cwah. Make one better than mine. Then, build your own, bolt on, very sturdy rack to go with it. This will be fairly easy, and prepare the way for you to weld your own deathbike, or your full suspension concept.
Next winter, we expect big things from you, after you learn to weld.