I see similar discussion all the time over on the SuperDuty board I read, never expected to see it here.
Don't take this wrong but I see this as a "do you think it can do it" instead of "do you think I should becasue it is safe to do it" question. Yes, it may be able to pull the weight, and yes it may be able to sort of stop (you said trailer brakes, 1 or 2 axle?) but is it safe in an emergency situation? I would have to agree with the others, I would not think it is. Be careful about justification based on what you have done or are doing. Just beacuse you are working now does not mean you are not past some limits and have just not gotten bit. Think of it as this way, eventually you will blow out your stock 150K bottom end running 25 PSI with all the bolt on toys you can afford!!!
I would be willing to bet the turbo 6 can get it rolling but I would guess you would have to be in the boost to get started and to accelerate. Hard on the turbo, but heat up the oil real good (extended loaded use). I would think you would be rather hard on the trans. I know they can be built to hold up behind a hopped up 6 but think of making it hold up under extended load with the weigth of 2 cars plus the trailer.
As to suspension. New GM trucks are coil, did not know that? All I have to say to that is all springs are not created equal.
Not a bash, please don't take it that way. Just be safe, I don't want to see anyone hurt. As a note from my experience. I pulled my TTA to the TA Nats last year on an open trailer behind my late model V8 Dakota. Truck, 2 people, all our gear, trailer, car. 3 hour drive, I fought it every step ot the way from minute 1 to the end. The trailer OWNED the truck. I would be willing to bet the Dakota is heavier, has more power, and much larger brakes than your ElCamino. That was the last time I pulled a car with the Dakota.
Brent