I hate 320 distributors, they do all sorts of weird shit, that is why I wrote this article.
I have a MG Midget distributor with a Crane ignition system on my positive ground truck, I went this route because I could keep it positive ground.
I also made up a Matchbox distributor for the same truck, I used a very slightly modified J13 distributor mount to mount the matchbox, the only thing I didn't like about that setup was that the distributor drive key didn't drop into the drive shaft as far as I would have liked but it started and the engine ran fine, my NL320 has that setup to this day without any issues, Mike showed how to do the mount plate in his NL320 thread, look at the first page, the 320 mount will not work on this distributor.
I bought this distributor for my RHD U320 as it has to have a side entry cap as the steering column is in the way, I have yet to use it/mount it.
This one will likely work and has the mount plate on it, but I don't know the brand.
That Lucus one you picked I know nothing about, it has points so it doesn't interest me.
The high energy power spark will also likely work and it comes with everything including the mount bracket, that is likely an install it, start it, time it and go.
Keep in mind that the Matchbox and that used MG Midget distributor with the Crane ignition I have mounted on my engine and I ran were both in my garage, I never drove it father than a couple blocks, the Matchbox Mike mounted in my truck when he owned it has been driven daily when he had it and I drove it a lot at first and it runs great.
320 distributors are hard to find parts for, and the parts that can be found are expensive, these MG distributors have aftermarket support, the distributors made to fit MGs that are not made by MG have aftermarket caps/rotors, and I don't know where one gets them parts.
It's all about doing your homework, I figured this stuff out by accident, I pulled a distributor out of a MG 1500 block and blinked several times, I then got my measuring tape out and started measuring stuff and when it looked the same I tried it and it worked to my surprise.