Length of lever arm.FJ40 net weight is 3500 lbs and gross is 5100 lbs. So 2 big guys plus’s their gear in and FJ40 is about max.
Late 80’s Monte Carlo curb weight is 3200 lbs, and with two big guys plus gear would probably be in the 5000 lbs range.
Unless you’re into a Chevy conversion with High HP, I think the JT adaptors are fine. My biggest worry is bending of the brackets during hard braking.
Also, if you go with the Monte Carlo brake option on all 4 corners, a proportioning valve and residual valves are included in your upgrade.
I run the Monte Carlo brakes without power....takes some peddle effort....but will lock up and you can feel the proportioning valve relieve just as the rear gets light.
The weight comparison only works if you’re running the same size of tires. Say both with 24 inch tires. Given a 40s stock tires are around 29” and most are sporting 31” of 33” tires, the brakes force is significantly less. A quick calculation would put it at 25% less than a Monte Carlo.
I’d want more not less. With 4 wheel disc’s using Toyota in the front, Blazer callipers & rotors out back, 80 master & booster, I’ve got way more. Braking is awesome... I’ve easily stopped my 4700 lb 40 towing a 4000 lb trailer without needing any brakes on the trailer. With a jab of two fingers it’ll lock up all 4 wheels on dry pavement. With steadily applied pressure they are very hard to lock.
To each his own... but I feel the cheaper, stronger, more powerful option is better. I’d go that way every time.