I feel like the standard weight of the ACE/Cobra body, even with fibreglass and space frame, hovering around a metric ton in 1955 is way, way too heavy for that kind of car. Especially considering it’s not considerably bigger or wider than the also-1955 Mini body which can go under 650 kilograms comfortably.
Maybe the current base weight values should be transferred to a second, longer version of the cobra body, and this current one made considerably lighter for Ginetta/Alfa Romeo superlite cars. A Ginetta G4 of similar size could even manage to be around 450 kilograms.
References to denote its diminutive size;