swap out the slant 6

Check out a Mopar Muscle or Mopar Action Magazine you can find at any magazine stand... A company offers the motor mounts needed to install a Small block 318 into your 6 cyl car. This could make it much easier for what your looking for. Build your 318 stock with a four barrel and a set of headers maybe a mild cam! should be what your looking for! you will also need to find a 904 or 727 transmission used for a small block... I would bet your car has a 904, I would find a late model Chrysler product with a 904 used behind a small block 318! The 727 if used will require a diff drive shaft! using a 904 your small block and tranny will bolt right in with the special motor mounts you can buy!, I would buy a new set of U-joints for the drive shaft since you plan on tearing up some tires!
Some other details may be in order to make this project work! nothing serious but some small details will need to be made with equipment change such as! Engine linkage, distributor Points/Elec ign, header's/stock A-body Ex manifolds, a stronger rearend such as an A-body 8 3/4 or 9 1/4, I am not sure what years these little rearends were used, but your car could have the 7 1/4 or 8 1/4rearend which is not very strong when burning your tires, so your current rearend will work but could give you problems after a few burnouts, anytime you start building somthing to tear up tires stronger parts are needed. If your not sure of what rearend your car has, find the numbers near the front of the center housing near the drive shaft, someone on this site can help you... you could be lucky and already have something strong already. I did see an 8 3/4 in a 1970 four door A-body 6 cyl car once. the car was ordered that way or changed at dealer to be used for hauling a small boat or camper! Good luck and I hope my info can help!