Sorry Bob.
The difference in the L30 & L31 is the L30 is a 305 & the L31 is a 350.
Like Dave said above, I have seen some quality control problems from GM crate motors in the last few years. Still I think it's better than or at least as good as the quality control from any other rebuilder out there. I think all of the small block crate motors GM sells now are brand new and not rebuilds. I could be wrong about that, but I can check tomorrow.
IF you were to have an issue, GM will cover the parts and labor to make it right......and that's not just at the place you bought it from, but at ANY GM dealership. Getting an engine warranty covered from ATK, Blueprint, Jasper, etc. can be a nightmare not only for the owner, but for the parts store you buy it from too.
The main reason I recommended checking with your local dealer was to see if they could match Summit's pricing for you. That way you could avoid the shipping charge from Summit.
To add another point to consider: (You can thank me later Bob.)
While Summit will probably charge you the $99 oversize fee, since they are out of state for you then you won't have to pay sales tax. That would cover most of that oversize charge and may make it worthwhile to just buy from them. I didn't think about that earlier.