how big? cylinder heads

Edelbrock will recommend a head gasket for you, as well as plugs.

This would get a better response if it weren't in the classified section.

I don't think this is getting many responses as its in the classifieds section.

To be on the safe side, you would want to measure the valve cuts to make sure. If its a stock piston, someone would probably be able to answer that but I have no idea. If they are aftermarket, they are more than likely okay as they would be a minimum of 1.94 for the intake, 1.6 for the exhaust (not every aftermarket piston but most).

As far as new heads are concerned, you are going to need something small. I believe the stock 289 chambers are 54cc. You need this size chamber on an iron head and roughly 52cc for an aluminum to compensate for expansion. This a bad idea on any aluminum head as most are cast at 58-60cc. If you milled the head that much you would have intake alignment problems and if wanted to switch heads, few people want a chamber that small.

IMO, I would keep your 289 heads and learn to port if you have the time or have someone port them. An average good port job would be around $500.

The generic 289 head gasket is the 8542, the "hi-po" version is the 9333.
I believe the 8542 is a compressed thickness of .039" while the 9333 is .047". Slight loss of static compression but both good head gaskets.