I have a 1998 Camaro with a normally aspirated 3800 II V-6 motor ("K"- VIN). The motor hardly ever uses oil nor has given me any problems before with 150K miles on it.

Experienced a significant overheating event (teenage son driver) and after allowing the motor to cool, I replenished the antifreeze / water in the radiator & overflow. 

First thing I noticed was the motor ran extremely rough and had water literally drooling/misting out the exhaust pipes. Looking into the radiator (motor running), it looked exactly like an old coffee maker! Nothing but bubbles...

I went ahead and followed my son home as I figured any damage was already done and there wasn't any need in calling a wrecker at that point as long as it was still moving under its own power. We didn't have too far to go & I told him to pull over if the temp gauge maxed out.

It did of course...  Good thing I brought lots of water!

On the drive home, I figured it was hopefully either a head gasket or head problem. Either way I'd be pulling the heads. 

With much skin loss, I finally got the heads removed. (How I wished I was wrenching on my old 67 Big-block Chevelle I had back in high-school!)  When pulling the heads I also removed the water pump, it was shot! So there was the overheating culprit...

Went down to the local Auto Shop and ordered remanufactured heads. Specifically telling them the casting #8134 on the heads, as I know there were quite a few heads made for this motor depending on the year model / VIN.

Got a call last night that the new heads were in so I sent my son down to pick them up. Of course I had to trade in my heads as a Core. $400 later my son gets home with some nicely boxed heads from a company called Dover Cylinder Heads.

I open the box to inspect them and they are nicely done and look great. Then I look for the casting # and about choke!

It's NOT #8134 but #4781...

Once more I try the Haynes manual but again it's of little use.

Are these heads interchangeable or must I have them shipped back and wait another week for the #8134 heads?

Yes, that casting number should be interchangeable as long as you use them in pairs.

There were six different cylinder heads used on the 3800 starting from 1988, seven if you count the old style head on the VIN 3 carryover engine that was used in the ’88 LeSabres, but some of the differences in the later heads were just minor changes to the same basic casting. 

Your VIN K/2 heads from 1995-’08  Series II engines got all new heads that had heart-shaped chambers, bigger intake ports and cast roller rockers. There were several castings including the 478/4781/8134 and 2261 that are all very similar, but the intake ports on the 2261 are slightly different, so we always use them in pairs.

 Good Luck!

 Brendan