Timing issue

[CARR33]

Just finished installing a 355 in my project. I timed it at 10 degrees btdc and it ran terrible. Timed it the old fashioned way, advancing until it pinged under a load and then backed it off a little. It ran fine but when i checked it with a light it was at 18 degrees btdc. It has a cloyes chain set. If i used the wrong keyway that would account for 4 degrees. It has a comp cams 268 xe cam, performer rpm heads and intake, dui dist, a 600 cfm carb, hedders, and 10.25 to 1 comp. Should i pull it apart to check the position of the bottom gear or leave it alone? It also has a fluidamper balancer that is new.