Okay, just double-checked the math and there appears to be a difference in the way Big Mauler is calculated:
261 pass blocker
262 run blocker
271 big mauler
239 zone blocker
According to the method of merely adding together the 3 components for each 'Type', LT Bushrod
should be a Big Mauler 'Type'.
However, he ends up as a Run Blocker 'Type'.
One potential theory is that height and/or weight DO have something to do with the player 'Type', at least in the case of the Big Mauler 'Type'. [for the record, LT Bushrod is 6'5" 315 lbs, so he doesn't exactly seem underweight...]
An alternate theory which I believe holds more potential is that there is some sort of additional 'limiter', probably related to the Strength stat.
Big Mauler claims to take into account primarily Strength, Run Blocking, and Impact Blocking. Perhaps to be considered a 'Big Mauler', your Strength stat has to be the largest of those three stats? So, if it comes down to being either a Big Mauler or a Run Blocker, if your Strength stat is 95 and your Run Blocking stat is 90 and your Impact Blocking Stat is 90, then you end up Big Mauler 'Type'?
RBK: 93
STR: 91
IBK: 87
Bushrod's Run Blocking stat is the highest of those three. Perhaps if Strength is higher than Run Blocking, you're a Big Mauler 'Type'?
One more alternate theory is that it's potentially bugged and you can't get a player's 'Type' to switch TO Big Mauler 'Type', but I think I've done it before with at least a few linemen (or switched a Big Mauler 'Type' player to a different position and they retained the Big Mauler 'Type', either of which would invalidate this particular theory).
I'm about to sift through the O-linemen on all 32 team's rosters, so I'll see what I come across.
At this point, Pass Blocker and Run Blocker seem pretty straightforward.
Balanced is unknown, Zone Blocker is unknown as of yet, and Big Mauler needs a bit of specific research.