I would recommend HP all the way for this. By far will have the broadest community of folks online who are willing to help when things go wrong or you need a part, besides having service documentation available.
If you have the space, consider an 8568B. 100Hz-1.5GHz, it tends to not be as desirable as the 8566B and thus can be had for cheaper (which is a shame, because the 68B has it beat in some specs, like phase noise). It will allow you to easily see all your harmonic content for the frequencies you're interested in. Very nice box, and it has two inputs, one DC coupled and one AC-coupled input that's rated to 50VDC (I would not recommend approaching this rating, but it could save you from an expensive mistake).