Okay. There's a lot to consider here. Robert's idea for glue on parts may be the best all around solution. I started testing different shapes over the classic chassis. I had no idea Marklin updated the chassis, which of course, complicates things. I would need to get my hands on one to test fit my designs. Ignoring the newer chassis for the moment, I've come up with something that may be good enough. If I make many different domes and parts and put them all on a sprue and make a brass base shell, voila.