29 years after a rebuild....

'Worn out' would be in the guides and seats... no big deal in putting in new guides and installing seats. Very probably the cheapest route.

Since you like numbers and math, here are some numbers for other options, all of which I have computed here based on nominal dimensions (I don't just throw numbers like these out). Some verification of the amount your pistons stick out of the heads would be needed before final decisions, and I have assumed these are flat top pistons with 2 eyebrows (standard higher compression 340 types) :

• Your present CR is actually around 9.4-9.5; the 'advertised' numbers back then were typically .5 to .75 higher than reality.
• Your present dynamic CR with your cam at nominal timing is around 7.1. So you probably never had any detonation issues with the present setup unless you got bad fuel or your ignition timing was out of whack.

Any closed chamber head like the Magnums or MA-X or LA-X, are gonna require a thick Cometic head gasket. For example, a Magnum with 62 cc chamber and a .060" thick Cometic head gasket to get to a nice quench gap of around .040", which would put static CR right around 10.2-10.3. Dynamic CR will be in the high 7's with your cam at nominal cam timing, which is fine on pump premium. But you will have to swap out the rockers and such to Magnum's, and swap the lifters and pushrods for oiling through the pushrods.

Or you could go with the new 'latest & greatest' with Trick flows and have nearly the same static CR with that type of thick head gasket; a chunk more in $$. Dynamic CR's would be in the mid 7's. You could use the present rockers. Push rods may not be the right length; IDK on that.

There is an Edelbrock AL head ''open chamber' version that has a recess milled in the head that is .060" deep in the round shape of the cylinder; that is meant to be used with the stock-type 340 pistons that stick up out of the deck. It is PN 60179. The breathing will be a distinct step up from what you have. Jegs has them for about $720 each with the standard flat tappet valve springs and a $100 discount on a pair. You'll end up with around 10.7 static CR with these heads and a .028" thick head gasket, about 10.4 with the .039" thick 1008 Felpro head gaskets, and right around 10.1 with the Felpro 8553PT standard kit head gaskets. So you can adjust the static CR where you are comfortable. Even with the thinnest head gasket above, your dynamic CR will be 8.1 or 8.2 even at sea level, so that is runnable on premium pump fuel.

With your slow ramp cam and modest lift, the stock Edelbrock springs ought to be OK. Valve lift is good to .575" for those. I have not looked at the other head option for springs at this point, but I am sure there are good options.... you cam is not challenging to any run-of-the-mill 'hi-po' spring..

Moving up to around 8 for dynamic CR with any of these combinations needs some attention paid to ignition timing but it is quite doable with pump premium.

If you are interested in doing these computations, I can share the program I like to use.