Take a look at this thread:
http://videokarma.org/showthread.php?t=268392
I was able to use a mixer to heterodyne the B&K 415 45Mhz sweep output down to 25.75 Mhz low band IF frequency. Feed the B&K 415 IF output into the mixer, add a sine wave of the needed frequency, and out comes the low band IF frequency sweep. I used an Analog Discovery II to show the flatness of the sweep, but you only need a regular o-scope for the B&K alignment process.
Dave