I'm pretty sure that the 1250 gaskets caused me big problems with stock sized ports. It's been 8 years or so, but I recall that when I dropped in an iron head GT40 crate motor with a stock manifold, the 1250's caused a major vacuum leak under the manifold. The problem was that the port sizes on the 1250's were much larger than the stock sized ports on the stock manifold and iron GT40 heads, and there was a gap open below the ports under the manifold. I remember buying the 1250's because they were "racing" gaskets, but the motor ran like it had a big vacuum leak -- which it did. It took a while to figure it out because the leak was under the manifold, but when I switched to stock Felpro replacement gaskets the problem was instantly solved. The stock Felpro blues are pretty good, so I'd go with those on stock ports. I think if you hold the 1250's up to the port surface of the heads, you'll see what I am talking about -- the bottom of the gasket below the port will probably come real close to leaving an opening into the lifter valley, and on my car it did. Also, don't use the rubber or cork end gaskets that come in the set, use the black gasket maker goo method. Good luck.