I need crown for my IWC

I received a gift from my aunt, this IWC watch. I want to keep for myself. Is my second IWC and I love it.
I need help to identify what model, characteristics of crown do I need for this watch. Where can I find to buy this crown?
Please advise me if is better to polish the housing, or keep it like that.
The watch is working perfect and in the last 30 years nobody used it.
I need to know what strap is fitting for this watch (17x15)?.

I hope that photos are clear and you can give the best advice for the future of the watch. If are necessary more photos or measures please ask me here.
Thanks a lot.

Your watch is a nice Cal 83. "Date Your IWC" says the movement is from 1946 but the case is from the mid 1960's.

The case looks a bit like it was handled by a gorilla. If nobody has used the watch in 30 years, it certainly at least needs cleaning and oiling. If it were mine I would certainly consider sending it to Schaffhausen for service, where they could also replace the missing crown and greatly improve the condition of the case.

Yikes, who ever attacked the case neither had the correct knife nor knows the meaning of the word subtle. The movement looks to be easily made good, the case is another matter. This is a job for the factory and may take several months.

Yes, I know that case looks bad, that's why I want to do something.
But please I need technical information, codes, about the crown for this watch, and the size of the strap? I want to search to buy and I need to know what I am looking for.