You should disregard this layout and not use it. Your entire B+ circuit should be linear and not have any parallel offshoots like we have here.
When you build a house you don't assemble the roof before you assemble the foundation. You don't install doors before you assemble the walls.
This is why you should not use a PPIMV, instead you should use a standard master volume. You should not use an FX loop. No FX loop should be in the amp until the base circuit works flawlessly. Build your foundation. Test it thoroughly. Only then add your bells and whistles.
The Input jack should be connected to the chassis. This is your earth ground. Meaning it's physically connected to the earth. This in turn should go to some kind of ground plane. A bus bar is common. Each node's ground is connected to this bar. From the rectifier ground to the input ground. The HV ground is the rectifier ground. This should not be connected to the power transformer mounting nut. Why? Power transformers get warm and this heating and cooling can loosen the mounting hardware over time, cause the ground to disconnect.
If your HV winding has no center tap, then you use a bridge rectifier, like in the diagram I made above. If your HV winding does have a center tap, then you use a full wave rectifier instead and the CT is grounded just as it would be with a bridge rectifier.
Fender amps had a steel chassis that you could solder to, and they would solder the rectifier ground directly to the chassis. On a Marshall style build (an SLO is a Marshall style amp) the rectifier ground gets connected to the bus bar, as does each node.
The Presence control is the one exception. You can put the Presence ground on the bus bar, but sometimes this will cause noise. when that happens, just mount the Presence ground directly the the chassis, via screw, nut, and terminal tag. The reason why this noise happens on just the presence control is a bit complex, and it's not really important.
How you ground the speaker jacks will depend on what jacks you're using. Almost all designs just have the ground on the sleeve of the jack. In Marshall designs the tip of the speaker jack goes to the ohmage wire, whatever that may be. Often these will be like yellow, green, orange, purple wires all having the different output impedance. And then you have a
common wire, that's usually black. The common is the ground. The word common refers to "all the other things that are connected to it". For instance a DPDT switch will have a center common lug, but that does not mean that lug is ground.
Almost all amps did this, but early Fender tweed amps often soldered the common wire to the output transformer body. Once mounted to the amp, that wire would then be connected to the amp chassis, and the metal Alpha open frame speaker jacks then connected the jack sleeve to the chassis. This is not really a good way of doing it. Fender stopped this and started wiring up their speaker jacks so that they were grounded when not plugged in. Marshall never did this.
6.3v heaters can be arranged in several ways. The most common method is to use a heater CT if the winding has one, or an artificial CT. Many amp techs much prefer the artificial CT and will tape off the CT wire and use an artificial one instead. This is because the resistors will act as faux fuses should too much heater current gets pulled by one of the tubes for some reason. This can save a power transformer from getting destroyed. And it's a lot cheaper to replace a couple resistors than a power transformer. Another method is to use a humdinger, but I would advise against it until your lead dress improves.
https://www.valvewizard.co.uk/heater.html
A star ground is not a ground that is connected to a chassis. A star ground is a ground that has everything else connected to it, so that the ground wires going to it resembles a star. The grounds on the right of that diagram are chassis grounds.
A chassis ground and an earth ground are both different and kinda the same.
In principle, an amp should only have 2 chassis connections. At the wall inlet and at the input jack. And each should be at opposite corners of the amp. But there's a "where the rubber hits the road" reality where it's just not practical to put a cap can ground on a long wire to feed it back to the input jack. So instead you just ground the cap can to the chassis close to where the cap can is mounted. This was a "screw it, it's not technically right, but it works" solution. These days, modern amp designs should avoid cap cans, so the issue should be moot. Cap cans will not be made much longer, and they don't perform nearly as well as modern radial caps that are a fraction of the size, weight and cost.
But if your amp uses them, do what Marshall did. Ground the cap cans to the chassis right next to where they're mounted. Make sure it's on a screw, locknut, with a terminal. Put a drop of nail polish on the screw thread so it don't come loose.
If it's not any trouble, it's more ideal to mount the cap can ground to the bus bar. I've done this with my own designs, and it works very well, assuming the layout of the amp is better thought out than how Marshall and Fender did it back in the 60s
