Charley, The 741 works good on a larger dish if you want to get reasonable signals on both bands. I am using a (repaired) C2 LNBF on my 10' dish now because I get an improvment on C-band over the 741 I was using. Not much of a difference, maybe 2-4%Q average across the board, maybe a dB or so better s/n. I use a 36" Ku dish on a seperate motor and find it much more consistant (maybe the signals are a bit less but sufficient). Your 1.2m should give really good signals on Ku with a Ku standard or universal LNBF.
Ku was always a real pain to line up on the big dish... any breeze or if the satellite landed between two "clicks" on the positioner, I would get a poor signal. I suspect the issue is the apature of such a large antenna is so narrow on Ku frequencies that it's difficult to get the aim good enough to maximize the signal. If I got it peaked on one satellite, moved to another, then back again the alignment was off again. Likely a little play in the polar mount and/or positioner messes it up. It would work but not great.
The 741 is a good LNBF though and works well on C and Ku. I find it's performance about the same as a corotor II with good DRO LNBFs (my sig), and a whole lot cheaper. Note that I am referring to the standard 741, not the universal Ku model. To get functional improvment you would likey have to spend some real money!