It is plain that I too am missing out on something.

I have never heard of Linseed spontaneously combusting.
Bear in mind that the UK's main importer told me that Linseed is non flammable, and you can- "Boil It" without it catching fire.

This would suggest that it is the thinners or carrier, (the turps) that causes the problem. This would not appear the case with the stuff used here otherwise there would be warnings on the containers, general knowledge of the occurrence etc.

I have to admit to being a little concerned as there are jars, brushes, and mountains of rags scattered around my home workshop, and have been for years.

Anyone who is chemically gifted and who can explain the possible differences or the situations leading to spontaneous combustion would have his views well received here.

With regard to the hand hewn timber, there should be no problem applying the finish.
I have found that a hand sprayer to be ideal, avoiding the risks involved with snagging bristles or threads on any splintery bits.

I have been advised by the distributors of Wagner Airless Sprayers that these can be used with a Linseed turps mix without problems.