Don Terrill’s Speed-Talk

Just a general interest question -

Why did Chrysler use a bellcrank system between the pedal and booster - but GM used a straight pushrod through the firewall?

Spacial considerations? Improved leverage pressure?

I ask because most ‘universal’ boosters use the GM approach.

Chrysler didn't use bell cranks on their brakebooster setups in the (mid/late) '60s.
Early Chryslers, with the separated booster and MC setups used a different underdash setup.
You're probably talking about the smaller models from Dodge and Plymouth?
My '73 Dodge Dart indeed has a bellcrank setup. Mostly due to clearance-issues because the booster couldn't be positioned inline with the pushrod on these models.
Newer GM's had those 'quirky' tilted backwards setups. Probably because the brakeboosters had grown in diameter so much that had to look for other mounting options.

My 67 Belvedere had a bell crank linkage under the dash...with the booster mounted on the firewall.

It was originally a drum/drum 318 car.

Ok. I was thinking the bell crank in the engine bay that abled an offset booster. But that doesn't change much ofcourse.
If both arms of the bell crank are the same length then there's no leverage benefit.