How fast do you want to go?If its just for fun then start with the 406.I built a very very low budget 406 for a friend.Torker intake,bought used,750 carter carb,bought used,mild hydraulic flat tappit cam,small tube headers,3.36 gears,turbo 350.In a 1978 monte carlo the car ran a best of 13.30s at 99 to 100 mph. decent mileage for a daily driver.also it had stock 400 heads with a 3 angle valve job
Ive never tried 1/8 mile. I doubt you will hurt a mild 400 racing 1/8 mile.
the 383 has better parts if you decide to go wild.