Again, with those kinds of lifts, and that kind of failure, I think that it is highly likely that you have binding in the valve train.
First, that lift requires a competition head. Competition in the sense that the valve springs need to be much taller then normal.
The head needs to be able to accomodate them without the valve spring retainer and the valve guide coming into contact.
That means that the lengths of the valves need to be something like 1/2" longer then stock.
I think that if you look in that area, you will have found your culpret.
Incidentally, your engine builder should have advised you that the life of those valve springs is going to be considerably reduced over that of a stock engine because of the increased lift of the camshaft.
What does that mean? It means that in less then 5,000 miles, if that, you are going to need to replace them.
The numbers you quoted to me is nothing less then a full competition valve train. They simply do not have the same durabilaty as stock. The pressure of the springs at full lift alone puts the engine on the ragged edge. If I remember correctly (and that's a stretch for me
) some race engines require the springs to be changed after every run down the 1/4 mile. 
Also, any lift over about .550 the builder needs to be 1000% sure of the valve train geometry and that the valve spring retainer is not coming into contact with the rocker arm, because they have a nasty habbit of doing that.
Just my opinion.