I too have noticed with age that aligning decals has become more of a challenge, Eespecially when making sure that the national insignias are equadistance to each other from one side of the fuselage to the other. I bought a set of dividers from a artists/drafting supply shop and use those. What I tend to do is apply a decal to the port (left) side of the model, let it set up, and with the dividers measure from the edge of the decal to, for example, the rear stablitator. Then prepare the same decal to the starboard (right) side, slide it onto the fuselage, and while it is still moveable, gently adjust it to the same positiion as the one on the opposite side, using the dividers as a guide.