Hi jcarter!
Welcome to the 'Stovebolt Page'. If you hang around, there is a ton of information you can pick up.
I've got a 46 2 ton that's original and drive it around Winnipeg all the time. You can see it here:
http://www.geocities.com/jarge46/46_Chev.html This site is one you can look at for parts. They are in Penhold, Alberta. There are other places you can find from the 'Stovebolt Page' too.
http://www.scottssupertrucks.com/ The guys here will tell you about the engine and rear end questions you have, but from what I've seen here, most will say trying to go fast with these old trucks doesn't pay.
I've hauled 3 yards of gravel on my truck and the brakes handled it without a problem. I was on a country road and tried a 'panic' stop to see how they performed and I was impressed. Those originals should be OK for you if they are in good shape.
Hope to see you and your truck at the Pony Corral in Winnipeg some Sunday evening. There is another 46 1.5 ton that shows up sometimes too.
Good luck with the truck.
George
