With the chain adjust your axle so that the rear wheel is as far forward as it'll go.
Then fit the chain and mark which pin you want to cut it at
Remove the chain and grind the head of the pin and a bit of the link
Then put a pin punch on the centre of the ground pin with the chain sitting over a vise, have the vice open just enough for the pin the fit through when you punch it out.
Knock it through as far as you can, then bend the link on the other side and slip the pin out with the offcut of chain
Pretty easy, just don't cut it too short, measure it twice, make sure the chain is sitting over the front roller and through the rear guide.
Do you have chain oil too ? don't forget to oil it before fitting it
CDI mounting rubber usually have 2 or more slots to mount them onto the tag on your frame, and can be turned 90° so that the wiring is coming out the bottom, straight down
Spray the filter oil onto the filter before it's fitted, don't get it on the inside of the rubber flange where it sits on the carby, it can make the filter slide off the carby.
Don't over tighten the clamp either, it can split the rubber flange, just do it firm enough to hold the filter on.
Is your carby flange threaded ?
It looks like the nuts are missing from the side you can see in the pic above.
The choke lever, you could grind the corner off it so it opens properly if you need to.
That's a neat welding job of the manifold too !!