I would advise you to choose a cam with around 205-210 degrees @ .050. That is still better than a stock 350 cam and will give you plenty of low end torque which would be advisable for your application. The cam you mentioned would be more suitable for a higher performance engine built for a muscle car. I would recommend this cam:
12-305-2 - PURE Energy
The timing chain kit you listed would work fine. Roller cams require a cam button to keep the cam from moving forward and backward. That would not apply to you as you have flat tappet lifters.

As far as pistons, I would use hypereutectic pistons like Summit or Keith Black brands. Forged pistons are not necessary. If I was to upgrade anything, it would be the connecting rod bolts as they are the main causes of engine failures like the one you have--that looks like a rod bolt broke. . APR head bolts are very good but new stock replacement head bolts would be fine. The one thing that I would highly recommend is to have the rotating assembly balanced.