Since your heads have 7/16 studs, you have options on the type of rocker to use. Most guys use a roller or a roller tip rocker. Your stamped steel rockers are probably a Chevy big block maybe made by Comp Cams. You can purchase one and see if it matches what you have. Hopefully they are not an unbranded cheap aftermarket piece. Replacing the one broken rocker will at least get you running. Some of the other guys can give you a better recommendation than me when it comes to roller rockers.
Before starting you really need to know if your getting oil to the valve train. Best would be to remove the distributor and prime the engine. You'll need a priming tool specifically for a W motor or make one out of a old distributor. If you don't have adequate oiling you will continue to have valve train problems - wear, heat, failure.
Although your cam is relatively small in lift, you should check the springs for coil bind. Since you didn't build the motor, it's hard to say what springs were used. Your cam card tells you what Crane recommended with their cam and the specs of the springs. If it's the Crane spring, the cam card states it should have a blue strip. Might be an indicator. You can also measure the installed height. The list shows Lunati lifters with the Crane cam, so maybe another brand of springs.
Make sure you get the valves adjusted properly. I just follow the service manual and adjust them on TDC of cylinders 1 and 6. Simple and it worked for Chevrolet.
After all of the above is taken care of, then address the smoking problem.