I would not worry about the rods more to worry about what year engine you have. Some have good rods some have bad ones. Either way you will want to find out. I am no expert but i dont think the 4x heads came on the 455. I think they were 16 but some of the trans ams may have come with 4 x low compression heads. At some point pontiac just started slapping cars together with left over parts.
A little research my be in order to find out which engine you actually have.
If you really want your heads to make power i think butler will port them for you. Probably make a lot more power than a home port job. He may also have a better set of heads ported and ready to go if your looking to buy.
Butler Performance - Specializing in Pontiac Engines Heads and Performance Parts
I built a nasty 455 HO for my gp. The heads i had stock were some of the best heads after they were ported and these had some nice work done. But they were always a problem since the big ponchos love lots of timing and compression. Cast heads were always a tuning issue. They knocked when it was hot out and ran low et when it was cold. Alum edelbrocks fixed all my problems with one big swipe of the credit card.
Fyi when i was done i realised i could have gotten a turn key 800hp from butler for the money my poncho cost to build from scratch. More ifit was a chevy motor for the same dollars. You live and you learn i guess.
I just helped someone that was doing port work on a chevy head the thread is still current and has lots of great info from alot of ppl on the forum. You may want to check it out. " first time head porting" i think is the tag line. Too hard to paste a link with my ipad it reloads when you move between safari windows.
Here is some good info on the heads out there for pontiac. You will notice the 4x heads are not in the top 5 heads to have for a 455. They work and will make some power just not top of the mark.
The Ultimate Pontiac Head
hope this helps sorry for the disjointed post i had to do a few searches to complete so i kind lost focus.