Hello There,
I dont have the SLO but I do have the HOT ROD 50 (Not the Plus) The regular Hot Rod 50 wich is the same schematic only with different transformers as Mike himself told me. And moving the loop require the mods. And I did them, so here is whats need to be done, and also went further and made some other improvements. I dont understand electronics and Ill try my best to explain.
1 - The loop is placed right after the low input channel, the clean channel sort of speak. So what happens, even with strymon pedals (that I use, and can handle up to +8db of current) is that you dont get volume low, but the delay DOES get drowned by the the gain stages coming after, its just like plugin a delay right before a dirty amp, it works a little better but not the way the delay should sound like.
So the first mod done was, see where was the loop connected and we removed it. No change in tone at all, its just a trail closed cicuit. So remove the loop, close the circut and done, no FX loop and the preamp section stays the same, no tone change at all.
The arrow shows where the loop its connected, we removed it and closed the trail. Loop gone.
Ok so now we went ahead an put the loop right after the master volume, see the trail where the loop was, is now closed by the yellow wire, and the black wires is coming behind from the chassi and under the board to be connected to post preamp section
Ok now, the problem is, the loop is amplified in the first section, so when it goes after the preamp it needs to get its signal level back or your master volume will drop. So a new Tube was installed in order to do that, not involving the preamp, just for raising the loop level. Also now theres a KNOB on the back besides the send and return jacks that can control FX level, so this mini preamp was built just for that, that coopper plate will hold a Tube and its using one side of the tube to do that. The other side of the tube is beeing used for another level knob that will control the LOW INPUT of the amps volume. Since the amp has LOW and HIGH input and share the same EQ a relay was installed so I can use a footswitch to change "channels" without unppluging the cable, so I can dial a Killer dirty channel and when clean is needed i just switch to the low input, as the volume drop is huge I can just go back in the amp and raise the LOW INPUT channel level up so it matches the master volume of the HIGH input. Its like having 2 master volumes and 2 channels that shares one EQ and thats all!
Again no changes in the preamp section at all, we did all this playing as it was done, different guitars, different player etc and no tone change at all! So it can be done if you are willing to drill the chassi and you have a decent tech. I live in Brazil and this guy builds amps for 30 years plus, dumble clones, JCMs etc and he did it in 1 day, so its simple.
Plate that the new Tube will be installed, one side of the tube will control the volume of the low input, the black arrow show the pot installed for that
Relays installed for LOW/HIGH switching with footswitch.
So I have a Soldano, with "channel" switching, an proper FX loop right before the power section and control of the level both of the FX and the Low input so I can use dirty and "clean" at the same volume without messing around with the amp preamp or tone at all.
If anyone has any questions feel free to ask, I dont understand nothing about electronics but I can ask the tech and reply here.
There is still some soldering to be done and wire organizing. After all is done, with the knobs installed, footswtich ready etc Ill post pics back
Sorry for the grammar mistakes Im from Brazil and my english is a little rusty!
Cheers
Might just buy one and send it to Mike for the works 
