I've done this sort of thing for years on C-band. It works best on high f/D dishes, such as 0.4, and the ideal arrangement is to offset both feeds from center by the same amount. Assuming both of these are implemented, the loss on each feed is very small, typically less than 0.25 dB with everything tweaked. Ku-band is another story.
Back in the day I used to put two lnb's on lot's of 10 & 12 ft dishes for hotels. I pointed the dish at F3 & G5. Which were (IIRC) 2 degrees apart. The signals were analog VC-II encoded and the pix were pretty good. I even used these same dish set-ups on Digicypher II encoded signals. Set-up was tricky and I used a spectrum analyzer. One rcvr on each feed whilst monitoring error rates might work OK for setup.