Good thoughts there.
The 318 idea I like better and probably won't cost anything but a few peanuts in milage.
And you probably had on a very modest and mild build an easy 250 - 300+ HP.
I had a all stock 360 minus the 635 Carter and dual exhaust off the manifolds with twin cats getting a constant 19 - 20 in my old Dodge Magnum (Cordoba based car for those who don't know) A MSD fired the junk yard distributor w/vacuum advance replacing the lean burn. The rear had 2.76 gears rolling on 235/60/15's. The Magnum was listed at 3700 lbs and then I get into it (180lbs.) and of course, gas will weigh in. 4000 lbs. and it wold move nicely.