I have 155/80 R13 only becuase of availability and price at the time, but they are stock wheels. In threads gone by, others have used 185's but with some modifications of some sort that I can't answer, but would definately include minilites, nor can I attest to the space under the arch on a bugeye.
My tires were $20 each from a national retailer, so if it were me weighing the choice of nearly new, make it fit or $100 for proper fit....I'd go with proper, it's what the car was designed for with the best balance and performance in mind.
That's just my tuppence, good luck!