I'm not feeling too confident about that rear swingarm either.
I'm sure its nice and strong up and down but it just doesn't look like it can hold up to any side load with all the forces basically going to that one tiny shock mounting point.
Forks are meant for vertical up and down force, not side to side, and I'm not sure just wrapping it in metal will help enough. I've bent too many dropouts as a little ~100lb kid BMXing to trust a fork mounted horizontally with a giant motor in a heavy frame.
Intresting. Nice work. Looks like you could add some motorcycle or moped wheels with that kind of setup at least for the front depending on the type of forks you get & the width between them. Right now I just got a basic mountain bike suspension setup that I’m using hydraulic disk brakes for in the front of my bike. Used to have a triple tree fork but it wasn't disk brake conpatable & didn't have suspension which made for a rough ride. Always wanted to try using motorcycle or moped wheels because the roads are a bit rough in my area for a bicycle doing 30 mph or faster.
Wheels are the Holy Grail of the homemade build. Motorcycle or moped wheels are the way to go but, geez they are expensive. My compromise is using strong downhill rims (Halo SAS) laced 3x and soldered. You can get custom cut 14 gauge spokes cheap ($25). Costs for $36 12 gauge spokes surge to $85 or so. Good rims laced with 12g spokes would be close to moped quality.
I tried to be nice and tell you it's not a good material to build with but you dont want to listen. Others have voiced concern about other areas of your build, they don't know anything. People who weld all day don't know how to because they live in another country. Huge corporations plan for the best case scenario, not the worst. Uni strut is strong and perfect for building bikes and motorcycles but no one uses it. My feelings are hurt because you say so.
At bare minimum I would box that top tube if you don't want to replace it. If you have more of that stock and don't want to cut a long strip of something maybe just clamp another one on top facing down and weld em together to make a rectangle? It would greatly strengthen it to any rotational force, which C channel bars are terrible with.
They hold up great for direct up and down forces like your seat sitting on it, but as the video above shows the open channel makes it very weak for rotational stress.
Kawasaki's EX500 is made of square and rectangular steel tubing for the main frame members. It's an outside frame that encloses the engine and other related parts. this is a bike that weighs 400# and has a 44 h.p. engine that can do nearly 110 mph.
It's all good because it's tubing and not channel.
There's nothing wrong with rectangular and square tubing in place of round, but as the main spine of the bike, that hanging channel that's Swiss cheesed to death is not a decent structural member.
It's some tough stuff, absolutely stronger than even the old, great quality stuff that bikes used to be cut from. You could knock a man out with that, bicycle tubing (especially today's tubing) would crumble under some people's heads, but not unistrut.
It's a smart move, many people don't even understand how much raw torque is pushed through these frames which is ultimately what causes cracks and rips a frame apart. Think of just the gyroscopic forces up against the frame every time the wheel's position in space is changed, at high speeds (for a bike) that spinning mass resists being moved and starts applying that infamous 'equal amount of force' back into the frame, which flexes and slowly tears it apart.
Anyone who's had the time to playfully spin a wheel outside the bike and held onto the axle would have noticed by now the way it resists being turned, including even forcing itself into a off vertical position (tilting itself sideways) position in order to hold onto the gyroscopic spin with the least loss in the system. But anyway that event is resisted in the solid frame of a bike so that energy has to be dissipated somewhere, that's the stuff that helps kill a bike, vibrations are bad enough, but vibrating AND tensioning steel is a good way to rip it apart really quick.
So there you go, I can't prove it mathematically without too much effort that that strut is stronger stuff than bicycle tube, but I know that 60 feet of it in a bundle is a bit of an annoyance to carry, I'd think that the bicycle tube at a third of the weight wouldn't be so bad to move around, and in the back of my mind I'd be thinking of how much better commercial shelf tubing would be to make a bike with than the flimsy (and almost not even good enough for a bed frame for a toddler) bike tubing they are using now.
It's good stuff I'd use it if I had it on hand, I think another friend of mine used something fairly similar to fashion a few 212s into a few frames that normally don't hold those types of motors .