If you paint your alum car "correctly".. there should be no way to tell that the body is metal.
The interior door panel of the S/C was covered in black vinyl, glued directly to the inner skin of the door, wrapped over the tubing. The door sill of the body has no trim strip like the street cars, and is painted the body color.
The underside of the hood and trunk are also thoroughly painted.
Remember that
all S/C's were painted by SA in California; they were painted on demand, over a two year period... however the customer requested... so there should and could be variation in how details were handled... most have the hoops under the lids painted the body color, along with the inner surfaces.