"Next question. You mentioned earlier that the toroid should be in the supply line. Is it worth thinking ahead and adding an alternative layout into the PCB so that with the aid of ‘jumpers’ and alternative positions for the toroid, components can be repositioned? The time and space is available to do this, but could you give me a sketch or sufficient written detail to achieve this."
...... No.
It is worth you looking at the PCB layout I used. Note how thick I tried to make the power tracks. These will carry tons and tons of amps for a very very short time. Our losses over these can be quite high.
I tried to use as much copper as i could in this section between capacitor and transformer. Even the to220 triacs have wide pin spacing, so the track down the middle is as thick as I could get.... but also I use well over 1/16the inch or more of solder on all the copper tracks involved with the power lines... and embed copper into it as well.
Notice also, the tabs that go to the transformer and the main capacitor on the non-triac side are next to each other on a large land, your have a thin 3" track, when they could have been right next to each other, and so keep noise and transmission loss to near zero.
In short, I think you would do well to redesign the power tracks to use as much of the board as possible, with as much copper as possible, and keep the two in/ou tabs to the cap and transformer on the non-switched channel next to each other.... or if your cap has 4 pins on it's top, you could route the transformer direct to it, and have no board losses on that arm at least.
Yes it will work fine in it's current form, but if you want to push lots of fence, you need to keep the losses in the toroid only, that way you can control the losses so that you get performance and life out of the triacs.
Very high currents involved in the primary circuit.
..................oztules