Goody has 9.5 dynamic converter which helps lessen the affect of the converter grabbing and pushing through the brakes at low rpm ....... id be willing to bet you have a stock type converter maybe a little higher than stock and its grabbing sooner hence pushing through the linelock... getting up higher in the powerband (rpm's)will help the tires to break loose easier and the linelock hold.....
Stroker, i used to run a POS no-name 2500stall converter that was more like a 2000. It didn't spin up as easy of course, but the 318 would still go into 3rd fine with the linelock held.
Glad to hear it works fine! Any movement is going to need more brake pedal, unless your front tires are sliding..which is a possibility, but you'd have to be sure on that one. I'll go check out your marks, i've done some donuts back where you are talking about in the 'Cuda before too!
Also that line-lock is recommended not to be held on for more than a minute (LONG burnout), just remember to switch the thing off when you're done. Glad to hear its working, we can tinker on that carb some next time.