How good are the Summit and Jegs 302 Blocks?

afaik it is just a stock unmachined block?

Those are fully machined (by fords production standards) with cam bearings, but the bore might be a little under 4.000".

They are the stock replacement thin wall cast iron production block. They are fine for a mild street car, but if you are trying to build a bulletproof shortblock for a power adder, or just high rpm, it will be the weak link.