line in on a Hammond PR40 Tone Cabinet

[spy]

I'd like to add a line in on a Hammond PR40. As you can see on the schematic the input G1-G2 is balanced! There's a simple way posted at Hammond Wiki but I prefer to go with a safer/better way. I'm thinking to add an interstage transformer but I have no idea about the primary/secondary impedances needed for this. Will this, Monacor DIB-110, do the job or do I need something else? Or stick with the quick-down-'n-dirty-but-it-works-and-is-harmless-Hammond's way ?