are these good heads (C90E's)?

[Unit 5302]

The 351W heads are nothing spectacular. 1.84/1.54 valves if I remember correctly. With the work, they probably flow pretty well, but they will still fall short of most aftermarket aluminums and irons. It all depends on the amount of work done to them.

Pretty much it's the fact they use different sized head bolts, 1/2" vs 3/8." That, and there are some of those minor water jacket differences.