The early 750s were 530 then switched to 630. Possibly later they again used a 530 on some models, I'm not sure.
Edit: Per J-Rod's comment I did some research, I am not a Honda tech specs expert.
Looks like the 530 was used from 69-76, then supposedly switched to 630 for 77-78. However, there are many 79 models out there with the 630 set, I will assume simply because Honda used them until they were out of them but who knows.
Now that I think of it, I owned an 81 and it had a 530.
The conversion is worth every bit of research it takes to get the right sprockets. I would call cycle x and make sure their 520 set is a bolt on for the 79, which I am 99.999% sure it will be.