The fx loop is immediately after the output from the 22k resistor and before the output jack. The original Guvnor used a single stereo jack (switching) so tip carried send and ring was return (or.vice versa): This required the use of a single stereo Y-splitter cable to connect pedals into the loop. This is a bit of a hassle, so if you're building your own I'd suggest using a pair of mono switching jacks instead, with the switched contacts of the send and return connected together.
The layout for the Guvnor here at tagboard can be easily modified: It is almost identical to the schematic of the OG Guvnor, but seems to be converted to true bypass. Two mono switching jacks for the loop could be wired up using the diagram in the link below: "send" from the board is from the blue output wire on the vero layout, and return goes to the bypass footswitch where the blue output wire would have gone.