I am planning on changing from a flat tappet hydraulic cam to a hydraulic roller cam in my 350 which is being stroked. I am using a 4 bolt main block from the early 70's. What changes will I have to make in the timing gear area for holding the cam in place? Will I have to use a special button and spring with a different type of timing cover or just the standard cam plate? Also do I have to change the distributor gear. I have heard so many things that I was wondering what others have done. Thanks
Rodney

See the attached article. Retro-fit roller cams require a cam button to limit the travel (.003" to .005") from front to rear. You'll have to see if your current timing cover will work with a button and the required clearances. Mine did not and I went with a billet after market cover that had a nice boss where the cam button goes.

You will need a "button", unless the cam is machined for a roller type thrust bearing on the plate to hold it in.
You WILL need a bronze gear for the distributor, unless you enjoy getting stuck in the middle of BFE with a stripped cam and dist. gear. Roller cams are made from a much harder metal than a normal cast cam. If you run a machined cast iron dist. gear on a roller cam, it WILL self destruct both gears... The bronze gear is much more forgiving, and will survive without damaging the cam.