If it were mine....
I'd take the time to do a little test, -it might be worth the peace of mind just knowing what is going on.
I'd pull all the glow plugs (to prevent hydrolock, -and give a visual indicator), -and pressurize the cooling system and wait.
Let it sit for a good hour or two with 15 or so PSI on the system. Make sure the fuel shutoff solenoid is UNPLUGGED, -and have a friend whip the thing over with the starter while you watch for mist out of the glowplug holes. That will at least give you an idea of which side the problem is on. You can also keep a very close eye on the oil level too, -although you may not be able to detect any level increase, -especially if the leak is slow. A trick I often used on some of the gasser stuff I used to work on was to wait overnight, -then very carefully loosen the drainplug, and see if you get any green stuff. Waiting overnight gives the oil and coolant time to separate, -and the coolant always ends up on the bottom, -which does make it easy to drain off!
I know, -other guys like to use the "see which side of the crossover the bubbles come out of" method, -that'd work too I suppose. I personally like to see which hole is seeing the coolant, -not that it really matters much.
If your block is original, -it would be a 599, -and they are not typically known for cracking (on the topside anyway). The bottom is a different story. I seriously doubt you have a cracked block on your hands.
More than likely, -you are probably dealing with a slightly pushed out gasket on either #2 or #7.
The heads? -you have every reason to suspect them.
As far as the oil analysis, -a good idea, -but if the oil level isn't going up, -and it's clean, -it's pretty obvious what's going on there. Hopefully you're still running the green stuff, -'cause Dex tends to make a huge mess of the oil in short order.
At least you'd be able to find out which side it is, -and pick on that side first.
Obviosuly, make dang sure you aren't dealing with something silly like a small coolant leak somewhere (another benefit of doing the static pressure test). It is amazing (especially on a dirty engine), how much coolant can be absorbed by the caked-on goop, -hence, it won't always show up as a leak in the driveway, -and you'll immediately think the worst, -like you're doing right now. Sometimes a hose deteriorates, leaving a clamp loose, -etc.
Start with the easy things first, -then the move on to the hard things.
Those coolant tabs? -They have done miracles for me and many others in the past, but they will not fix a head gasket or cracked cast iron. Sometimes they will buy you some time.
My .02
