With the old engine that only made about 540hp/590ftlbs, it hooked ok with 285 65 15 BFG drag radials. Not the best, they only did 1.7ish 60fts. This new engine smokes them like its on ice, half throttle smoke shows are the norm now, but those tires are old and hard. Bought them in 2002. Here is a half throttle vid before I got the body put back together after paint.
Slapper bars are really only intended to stop wheel hop, which should be hard to get with multi leaf springs. Mono leafs will hop around easy with enough power and some traction. To really hook the front end needs to come up somewhat easily, and if you can get the rear to lift instead of squat that helps too. Calvert bars or lift bars are the ticket to get the rear to go up. The lighter up front the better. Without sticky tires you are going to be doing John Force impressions with a 455.
My 70 GTO with 2.93 gears and stock converter in the Th400 would spin the 275 60 15 Kumho tires hard while rolling 35mph, it had a low compression 455 that made around 500ftlbs and approximately 400hp. That year Goat has a 90lb front bumper, so they are fun to get to hook.
Most Pontiac 350s I have been around can have traction issues easily, they have the same stroke as a 400's 3.75" with a smaller bore. They like to grunt with that crank. As a side note, its super fun to tell a chevy guy you have a 350 crank and rods in your 400 and its a 406. They get really confused.
I like these engines because you can run highway gears and dont need a big stall behind them, but they really like 2200-2800 stall. That means less stuff to buy, lower cruise RPM on the highway, and they use less gas because of it.