I have had a couple 4bbl slants, one rock stock, the other with headers only. The only problem I've encountered was that the headered one's PO had installed a 750 dp. So first thing I did, was try a 625 I had from a 318, still too big. So I bought an electric choke carter 500. Just right. I think a 400 to 500 carb would be just fine on a stock sl6.