318 BASE TIMING

So then what about a 5.2 magnum carbed? Ive got a stock 5.2 i put an airgap intake on and a 1405 600 edelbrock carb. I set initial at 15 and it ran like crap, i advanced it until it ran the best i ended up with 42 degrees initial! I have no idea. I Checked TDC (pulled number one plug and looked by eye and could see the piston at the top and measured also with a dowel).and the mark was correct it seems. plugged vaccum advance. I played with the idle screws on carb until it was pretty smooth. About 1.75 turns out. Is this a symptom of a jumped timing chain? Ill be tuning it alot this weekend any advice would be great. Thanks y'all! I really dont know what else to do but try another timing light. Ive Googled the crap out of this and havent come up with much other than confirming TDC and making sure timing light is good.