i have a 1964 plymouth belvedere that was passed down from my grandfather who bouth it new in 63.  the block was cracked by my stupid nephew who decided to run it without water or coolant.  i dropped a new 318 in it with elevated intake, 600 cfm edelbrock and flow max headers, and replaced the 3 speed on the collumn with a 4 speed on the floor.  i got 16 inch american racing rims (that resemble the old craigers) and some new tires for it.  

now comes the paint job..... i was thinking painting it a flat black or leaving it primer to give it the ruff street rod look. what do you guys think.

all suggestions welcome  

It may be worth it to investigate what the original paint and code is/was and paint it the original color it was when your grandfather took delivery. i think that way when you look at your car even though you made performance mods, you have shown respect for his choice of color when he bought it. a person's identity is not only with the make/model they choose, their identity is also in the color they choose it to be. so the original paint of the car most likely was his favorite color, or at least the color he thought he would look best in driving down the road. you will also show your family by restoring the original color that you appreciate/respect his gift to you  of a truely rare car.