I just bought a competition engineering engine plate for my 440. Its going into a 72 duster coupled to a 727.
My Question is do I have to run a mid engine plate as well or will the front plate and trany mount be ok???
Like Bob said, the front plate alone will be sufficient. The Mid-plates are really only necessary with big HP/TQ combos. Since you won't be using the motor mounts any longer, you should also consider using an engine limiter to keep the motor plate from flexing during hard acceleration. Without the limiter, you run the risk of cracking the tailshaft housing on the trans. S&W Racecars has a nice limiter kit for a good price.
I second the travel limiter and the poly mount is a great idea. I ran full front plate, travel limiter and stcok trans mount for 4 years on the street and strip in my tubbed duster and had no problems.
A engine limiter would go from motor to frame, to keep motor from moving front to rear. Here is a picture of mine. It is the gray rod , bolted to the motor mount boss, rod going to the front is bolted to the frame.
I want to suggest that you tie the engine down forward and aft with a front mount. As you accellerate the crank trys to go forward and when you let off it trys to screw backwards. It will make a tranny 3 piece at the finish line.
I made a mount off of the K-frame and tied to the front of the block but there are several ways to do it.