This is a simple concept for super heavies of the retro tech variety: the cockpit type and internal structure basically are heavier but otherwise functionally identical to their non-retro tech/primitive counterparts.
Primitive superheavy cockpit: Same in function as a superheavy cockpit but it weighs 8 tons rather than the standard superheavy cockpits 4 tons. Otherwise follows the same basic gameplay rules as the normal superheavy cockpit.
Primitive Superheavy Internal Structure: Same in basic function to the standard superheavy internal structure, but weighs 20% more(rounded down) per a 5 tons over 100 tons. Otherwise functionally acts identically to superheavy internal structure in terms of gameplay rules.