First up, what sanctioning body over-see's your track? NHRA, IHRA, or someone else?
Get your hands on a driver's manual for that track, and note the Sanctioning body's rules, and those of the track. (The tech for the car, and for you as a driver.)
On the bright side, these tech requirements are pretty easy to meet for a door car. You just want to make sure you meet them prior to driving out and paying your fees.
Once your car can pass tech, and your driver's requirements are in order per track rules, your on your way!
Most slant cars came with open rear ends. That isn't a show stopper when you employ a trick or two with tire pressure.
The deadliest cars at the drag-strip are slow cars. They tend to be more consistent. Not every time, but it's a general rule. If you want to win races, figure out how to cut lights. Leave the car alone.
Going faster is funner, but it doesn't win bracket races unless you can get the car dialed in. The Quicker and faster, the harder that gets.
If I was building a car for the street and strip, Higher stall Converter, bigger exhaust, like a 2-1/4" Feather Duster single, get the carburetor jetted in, and leave everything else alone. You might have an 18 or 19 second car, but you'll clean up if you can get your lights figured out. 90% of races are won at the tree. The other 10% are won when top end games are played. If you can dial your car, cut a light, and know when to stand in the throttle/brakes, your a bonafide drag racer.
Now if your building your car for bragging rights, then your going to need to build some power. There is no over the counter recipe for a slant six. There are some nifty parts, but they need to compliment each other, and there may be some prerequisite machine work required. With an engine of this displacement, if your tune is off, your going no place, no matter how much money you throw at it.
I was asked what I had done to my engine and transmission a couple years ago. I told the person it was easier to tell them what was stock. (The transmission case.) Yep, about it. Would I build a long rod stroker again? Maybe, maybe not. Are there other ways to do it that are faster/quicker? oh heck yes! Did I have fun doing it? Sure!
CJ