I have received this same question countless times over the last 15 years that my speedster has been on the road. And I found myself for the first time writing the response instead of telling it, so I thought I would post my perspective here.
My speedster is in the upholstery shop at the moment, and this is the best picture of the front brakes that I have. The car has motorcycle disk brakes on all four corners, and the plumbing is done in a conventional method with a single master cylinder. The brakes work very well, and so far have stopped me faster than I've ever needed to stop. I drive this car almost daily in fairly congested urban traffic, and I drive it like a modern car.
Now that being said, after 10 years of service and if I were starting over, personally I would not use motorcycle brakes again. As great as they might work, I am afraid the 1500 pound car is asking a bit to much out of the little brakes. I think if I drove the car more like a model T the brakes would have been fine, but my right foot is pretty heavy on both the gas and brake pedals. I don't have any problems with fading or insufficient braking, but I do suffer from rapid pad and hard part component wear. The motorcycle calipers float on rubber guide pin bushings and after a little wear they will start to wear the pads tapered and eventually chatter. After 10 hard years of service my brakes have wear beyond the point of servicing and I will be looking at replacing them in the future.
I have known several people who have had good luck using a more robust caliper and rotor setup off of a large motorcycle like Honda Gold Wing or Harley cruiser. But I chose to use lighter duty late 80's Honda street bike brakes because they are lower profile between the wheel and rotor, so I didn't have to space my wheels out.
When I get around to replacing my brakes I will be looking into some sort of hydraulic drum brake set-up. The brakes and a couple gauges on the dash are the only non-era parts on this car, and to tell you the truth the brakes stick out like a sore thumb. Personally I like what the brakes do, I just don't like how they look anymore. I highly recommend front brakes in any form, I just wish we T'ers had more brake choices available in a kit. I don't mean to rant about for or against disk brakes, I'm just trying to give my perspective on the topic for anyone who might be looking to adapt front brakes to their T.
Check out Speedway Motors http://www.speedwaymotors.com/
They have/had a disc brake hiding kit with a fake drum and backing plate for the nostalgia street rod guys that wanted to maintain the period look with a disc performance
From the view point of a parts maker, the problems with offering a brake kit are difficult to overcome.
1) Very small market
2) Product liability insurance for such items not obtainable at reasonable cost.
3) Market price unlikely to achieve even a "break even" amount.
4) Any successful setup that overcame the first 3 items would be quickly and poorly copied by all of the MTBC vendors leaving the original vendor to take care of tech support for all versions of the product that was offered.
Hmmmmmm, on the hunt for brakes an calipers. This is a clean setup and finding a heavier duty 'sport' set shouldn't be that hard.
The hard part will be welding on a bracket to keep here in line and spec tolerancing the caliper.
The unique thing about Kevin's set-up is that it fits, it works, it's afFordable and it has proven reliable.
I've seen the car several times in the past few years.
I agree, and aggressively driven speedster as well as a loaded touring car can use improved braking. My dad's speedster with 4 wheel brakes is way more manageable in the hills and traffic. But as Kevin points out, it is difficult to manage a system that works and is/looks period correct. Good luck with that.
Still can't believe how well that radiator shell turned out Kevin.