Would you suggest "total" rebuild on a 318 that has been sitting for like 15 years with the intake & heads off - apparently burnt exhaust valve(s) and previous owner was going to fix, but did not get around to it. Car has sat outside, hood down, in dry climate (well, as dry as canadian prairie could be) . . . being long time since seeing the car, so don't recall if the cylinders had rust in them, or on the cam . . . . thoughts ??

I would count on rust everywhere you do not want it. Are you asking what a rebuild would cost here?

No, just whether or not getting heads done, and cleaning up any "rusty" cylinders and put it back together . . . but I am thinking it's half apart already, so pull engine and do a rebuild . . .

Sounds like a case of "do it once, do it right".
That way, it's not a source of worry or bigger expense later.

If it's been sitting that long ...and it's partially apart right now...I think a complete rebuild is in order.
You will be glad you did in the long run.

Well, pull and inspect it anyway. Go from there.

You never know what you have until you pull it apart. Prior to that it's all speculation.

I agree 100%. And it's probably much worse than what a little elbow grease will fix. Cylinders probably need bored not just honed. Crank probably needs turned Undersize and lifters are most likely stuck in there bores. Plan on new oil, fuel and water pumps and maybe a distributor. The carb will certainly need rebuilt. If you have squirrels, chipmunks, mice, or birds there you are likely to find a big mess in the lifter valley and down in the cylinders.

Sorry for the negativity but that is what I would expect to see.
If you or someone else would just lift the hood for a couple minutes you will know whether to proceed or find another engine.

Rebuild

Yup, think I agree with everyone . . . do it once, then you know what you have.

Pull it apart. Is the chain real sloppy, bearings worn, ridge in the bore? Then determine its intended use. Everyday driver? performance? Light usage? If the walls and crank aren’t junk just fix the heads (or find a used pair), ball hone and through it back together. Many times a lot of dollars are spent to get it perfect. When in actual use you would be surprised what will work pretty well. Remember we are talking a 318 here.
Doug

If the engine is intended to be nothing fancy can you just trade it in as a core charge towards a new remanufactured one? There used to be some NAPA general engine machine shops around here that would take good cores in for common type engines - 350 Chevy, 351 Ford Windsor, etc.

Machine shops here are all jambed up due to lack of consistent parts availability so getting a whole engine done now takes months instead of weeks. Heck, at some of these places you have to get on a list and wait weeks to get it in the door.

That is what my initial thought was for this . . . it's just going to be "nice driver", not performance . . .