The problem you are going to have with painting another hood is going to be matching the paint. It is hard to match metallic paints at a later date because of the way metallics settle. If you can remember all the steps you used to paint the body, and can get pretty close to the same number & thickness of paint coats, then you might get really close to a match. One option would be to paint it like a flat or semi gloss black like some of the Mopar muscle cars had. Since it is a shop truck also, you could pretend the shop is upgrading its ride and have the custom hood in primer.
I don't know if I would give up on the big block motor right away, I would think about can you change the intake to make a stock hood (which I'm guessing you painted with the body) fit, or can you fit some kind of hood scoop to clear it?
Another option would be to find a custom hood that fits, try to paint it in the same color so it is close in color, then consider adding some kind of graphics or flames to the model so if the color is slightly off it won't be too noticeable.