Soulfused Construct has the following sections:

Hit Dice: The soulfused construct retains the base creature’s Hit Dice and hit points (but see Advancing a Soulspark, page 198).
Essentia Pool: The incarnum possessing the soulfused construct’s form gives it an essentia pool equal to 1 + 1 per 6 HD it possesses.
Advancement: By character class.
"Advancing a Soulspark" reads as follows:

A soulspark not created by means of the soulspark familiar soulmeld gains 1 additional point of essentia to invest in its incarnum shroud for each Hit Die it gains. Its Dexterity and Charisma scores each increase by 1 for every 4 additional Hit Dice.
This brings me the following question:
Q 486: Does the Soulfused Construct's inherited Soulspark advancement apply to RHD, class levels, or both, and does it apply only to those before the template, those after, or all?

For a 5 RHD, 7th class level Homunculus who had it applied at 3rd class level and purchased one of the RHD after, the results from this would be the following:

Spoiler: Homunculus 4/Class 3/Soulfused 1/Homunculus +1/Class +4
Show
Before After Both
Any HD +7 E, +1 Dex/Cha +5 E, +1 Dex/Cha +12 E, +3 Dex/Cha
RHD +4 E, +1 Dex/Cha +1 E, +0 Dex/Cha +5 E, +1 Dex/Cha
Class levels +3 E, +0 Dex/Cha +4 E, +1 Dex/Cha +7 E, +1 Dex/Cha

Note that Soulfused is LA +1, so it doesn't give an applicable hit die


To my recollection of t, the most likely cases are RHD before and class levels after, as the template is blatantly intended for Mindless constructs given the 3 Int and declaration of feats applied, but as it's referring to an Advancement section and declares the creature's new advancement it could be the obviously-absurd "your future Incarnate levels give +1 Essentia each". I give the 3x3 grid for completion's sake, "all hit dice ever" is obviously ridiculous as it results in Wilder-based Soul Manifesters or Sorcerer-based Soulcasters receiving far too much value for LA +1.