As we discussed through email, I like your plan. It is a similar logic to what I (and a few others have done). Fill your more classic, tubey needs with one head (for me, that is the Streamliner900, for you, it seems that is the RH750) and then a more neutral 'modern' need with another head (in my case, the F500, in your case, the LMII/III... others use a Shuttle 9 or whatever).
Nice combination that covers just about anything you will need to do. The actual product choice (e.g., for tubey,the Streamliner, a Mesa head, the RH750, the Orange Terror, etc.) is a matter of tonal preference, output need, etc. (similar to the choice of a Shuttle, one of the Markbass heads, one of the GK heads, etc., etc. for a more solid state vibe).