OK,
original cars (almost every one ever made) are built on a budget for profit margin and costs are cut anywhere possible. this does not mean it is the best thing to do. Paint is one of those, lets say, cost cutting areas. the underside of the car, the engine compartment, the underside of the hood and trunk lid, inside the trunk etc. If you want originality, you will need to do the same for points. If you just want a great looking/driving triumph and don't care so much about points in shows, give it the best paint job everywhere. Remember that the MOST IMPORTANT thing you can do is perfect prep work.Go ahead and clear coat if you did it on the outer body.
IMHO
Rob