That is TBer Vic's recommendation.
And yes, since I like the MB stuff so much, I've kind of forced myself to go to school on the names, and have played quite a few of the executions (I've owned the SD800 and SA450... again, like you, looking for that elusive 'LMII but just a bit more' magic).
The best way to think about it IMO is to lump the MB amps into 4 groups (ignoring the big tube head).
The 'LMII' sounding group: LMII, LM250, LMK, SA450, LMIII, LMTube. These are the class A/B power amp models (there are other ones with special features like tube compressors, etc., but I put them in a separate bucket) that have IMO that warm, organic but even and full tone that many LMII owners rave about. Power ranges from 250 to 500 watts RMS into 4ohms.
The 'SD800' sounding group..... SD800, LM800, LMTube800, SD1200. These are the higher powered class D amps, and have that more wide low end and more aggressive upper mid response to my ear... a 'less warm' tone IMO. The '800' name models are 750 watts into 4ohms. The 1200 is not surprisingly more powerful (haven't played that one, not sure when it will hit the US. I ASSUME it will be a more powerful but similar sounding SD800, but who knows).
The F1/F500.... my favorites... yet another, different class D power amp, and the tone is closer to the LMII than the SD800. Quicker and tighter than the LMII, and a bit more aggressive in the upper mids and treble, but much punchier and 'warmer' than the 'SD800 class' amps. The F500 is just the F1 with more features... identical tone. These are both 500 watts into 4ohms, but again seem to have a touch more 'ooomph' than the class A/B LMII class of amps.
All others.... This is my lazy way of lumping all the other executions that have stuff I'm not interested in... tube compressors/pre's (501/503.. which do have the nice LMII type class A/B power amp, but are more expensive with the tube type features), multiple distortion channels (Studio Pre 500), special hybrid designs meant to more closely mimic tube amps (R500).
What gets confusing is that the four new 'LM' heads are grouped together (IMO) based on footprint, not tone.
Whew.... a little compulsive on my part, but that's the way I keep all of these in some sort of 'tonal order'.
Edit: I wonder what the 600 watt Momark power module sounds like. If it's a more powerful F1 type tone.... whoa nelly!