What swingarm and hub will fit a CB350T from 1969?

Think this is my biggest change of getting a solution on my problem.

First of all, I have a CB350 twin from 1969.
I about to swap the fork on the 350 to a fork from a CB500 to get the front disc brake setup. On this 18" rim I know I can fit a 4.00 Firestone Vintage tire (have that setup on my CB500K3-77)

What I am now thinking about and cant figure out.....

I would like to have 16"x 3 rim in the rear with a 5.00 (at minimum a 4.50) Firestone tire. This is as I know a hard task due to the space in the stock swingarm. I know I might have to swap stock swingarm to another one.

1. ??? But, which swingarms are a "clean swap" without any big modifications at the frame?
2. ??? And if I switch stock swingarm to say one from a SL350 do I need to use the hub from SL350 to make it fit?
3. ??? Or can I just extend the stock swingarm and then it will all fit with a 5.00 tire?
4. ??? How how shall I finalize this?

As I said, I would like to be able to have that fat tire in rear with as little modifications on the frame as possible.

(I know the bike will handle worse. This is just for the look. I am a novice mechanic)

Had one older thread that handled some of this questions but didnt get the answers I needed, maybe due to poor english or misunderstandings.