School Me please

As many of you know I buy and part out alot of tractors, mostly IH and Ford. There is going to be a HUGE JD auction near me and when i can get ahold of JD stuff it sells great but i dont know anything about it. So i have some questions...

What is the difference between a styled and unstyled A and B? Will the parts interchange?

What are the A, B, H, G comparable in size to in the farmall family?

Thanks