Have a distributor that don't have a nipple on the advance timing. Can I convert current distributor to use the vacuum port or do I need different distributor with vacuum port?

 

You'll have to change your distributor. All you have now is the centrifugal timing alone. Having vacuum advance will almost certainly give you more HP and better gas mileage. Might be able to find a good one at a scrapyard. What year is your Chevrolet? Most came with vacuum advance from the factory.

You'll need to make sure the vacuum diaphragm isn't leaking, as they do wear out. That's simple, as if you suck on the vacuum port, it shouldn't allow you to have any air coming through. Changing out the vacuum advance diaphragm is cheap and easy to do, however.