Good choice. Remember all Pontiac V8 blocks are pretty much identical on the exterior, so nobody will ever know. PS, the pins on the back of the 400 emblems will not match your 326 hood anyway.

PPS: also refrain from the totally inaccurate practice of putting engine size decals on your air cleaner. Some enterprising smarty decided while reproducing Buick engine decals to change the Buick symbol to a Pontiac arrowhead and thus the uninformed Pontiac owners now all think they belong on their cars.