vpoppv: sorry for the delayed response - I didn't see your question (was
away sailing when you posted it and it got lost in the volume of messages).
The car has "unassisted" brakes like Dr Larry's car, but we didn't puncture the booster diaphragm. Instead we upgraded the smaller rotors & calipers from the 3-cylinder car to the larger caliper & rotors from the 4-cylinder car. The brakes are still firm, and a fair amount of muscle is required to stop quickly. (How hard? I wouldn't feel comfortable letting my mom drive it.) But it's noticeably improved over the "unassisted" 3-cylinder setup.
I'm reluctant to puncture the diaphragm because once I do, if I decide later to add a vacuum pump to reduce braking effort, it can't be undone.
I know Dr Larry swears by his punctured diaphragm method, but I'd like to hear a 2nd or 3rd opinion of someone else who's done it before I'd take that step.