I would do a general upper gasket overhaul with the engine left in.
140K is not alot of miles, but these cars generally speaking have weak head gaskets that could probabyl use replacing.
I would pull the heads off, and get them surfaced, and perhaps a valve job.
$250 would be a good ballpark guesstimate for a valve job and surfacing.
The "head gasket set" is about $120 at the part stores. Other areas you will want to look at to make your decision are the head bolts, as stock-type headbolts cannot be re-used, you either need new stock replacements, or ARP head studs. You may also want to look into MLS gaskets, just so you're informed, but on a stockish they're not really necessary; especially with a stock deck finish.
On secod thought, I'd do a "compression test" to be sure the rings are OK before doing this, I believe you can get a compression tester from the free tool rental at autozone... Od another search for compression test to see what is acceptabel and how to do this....
I would also switch to a thicker oil at this age also, some are even using 20-50 on higher mileage, stock engines. You deffinately want to keep after the oil pressure and level in an older engine. Not to mention a thicker oil won;t leak as much... Also, I've had some luck using the "stop leak" or "no leaks" (bars is the name I think) and every few oil changes I add a bottle, and it seems to have stopped/slowed a slow front seal area leak... It was dripping, after using it it, it was still damp just not forming drops under the car...
Another quick note, if you do the HGs, make sure you drain the oil, as not to allow coolant to sit on the bearings, as this is bad... So after you dissasemble the upper engine, drain the oil...
This is assuming now, that you are not building a high end "race motor" and donnot plan on lots of mods, and big boost, etc.
From the sounds of it, you're just wanting to freshen it up a bit...
You need to let us know what your goals are for the car to really be able to say much...