You are going to spend $3000 for a complete embossed Pepsi 81 since there is a long line of collectors ahead of you.
I think I know where your search started, you got a rusted transitional 56 and because it was painted blue you thought you should put those parts in a round top Pepsi machine.
Best idea is to locate a stripped Coke 56 R/T, weld the rust, paint and install your parts. Then sell it and use that money and buy the Pepsi machine of your choice.
Basically how my search went, but I don't necessarily need the parts I have to go in the machine I find as I can just sell em and get a complete machine to make up some of the cost difference.