Typical sized cars heres the formula ( yours would be worse)
Top speed (mph) 20 times cube root of horsepower
Example 400hp cube root is 7.36; times 20 is 147 mph
the hp climbs exponentially much high the faster you go aka drag limted
So your magic 340 was making what 550 600 hp @ 6900 with stock valvetrain gotcha
rusty would need about 700hp no problem with his magic low comp 340 at 4000 lbs
Some of us nostalgically remember our cars being faster than they were. A '70 340 Dart went 14.5 in the quarter. The fastest car back in high school (45 years ag) was low 13s and it had been heavily modded.