I'm in the middle of tearing an engine apart for oil leaks. The leaks I'm chasing have more to do with holes, cracks, and other casting defects, but I couldn't help seeing all the posts on this site about leaks through those seams that use only a sealer and no gasket.

Lycoming and Continental aircraft engines have been split down the middle forever, they go together without a gasket, and they are forbidden to leak oil (oil leaks lead to fires, which are not good in a fabric covered airplane way up in th sky). Granted, they have a lot more bolts around the perimeter than most other engines, but the big trick they use is a single silk thread carefully laid down on the mating surfaces before they go together. This thread runs all the way around the mating surface and crosses over itself when it gets back to where it started. The crossover is not a knot, just one end of the thread laid over the other at about a 30 degree angle with each end extending maybe 1/4" past the crossover.

Has anyone tried this with a Savage engine, either around the crankcase or the camshaft cover? I imagine a combination of this and the black sealer should make the thing properly oil tight.

Well .... almost. The rubber plug remains an issue. One day I'm going to thread that hole, fabricate a short bolt, and use a fiber washer between the bolt head and cylinder head.

I cant see how that could hurt a thing. Where are these strings available? I have just done the cam chain & used the liquid gasket sealer. So far, no leaks.

Coming from aviation maintenance myself I was surprised to see camshaft bearings in plain alluminium, where i was expecting a bronze bushing.
The sealing of crankcase halves or the like with liquid gasket is normal and will, if properly prepaired and applied will get the job done: Sealing.
On the RR engines we used to apply the blue stuff called Hylomar, worked very good.