What would you do? Slant performance
Congrats...Your now in the 16's. Lol
You get it, Johnny.... Naturally-aspirated, these things are just too much of an uphill battle to make it worth all that effort. Conventional hop-up methods don't pay off very well, for N/A slants; it's been proven, time and again.
There is only one way I am aware of, to get resonable performance out of a slant six (because the poor-flowing cylinder head defeats all you can do,) and that's forced induction.
Turbocharging, or supercharging a slant six isn't easy nor is it cheap, but it will put one of these motors in an early A Body, well into the tens at almost 130 mph, and that is pretty fast for an old Mopar... Hellcats need slicks, just to keep up...
If less speed is needed, it can be a lot cheaper and easier, using lots of stock components, such as stock pistons, rods cam and valve trains... but, that M.O., along with less boost will result is a lot less horsepower... but, not everyone wants to go 125mph+ in the quarter...
You pays your money and you takes your choice... :)