I looked into tanning the old school way and talked to some folks at gatherings of the primitive types that do re creations and reenactments and was told that there is a lanolin type content from that method of tanning that works better on Deerskin than anything else for pliability. Might answer some of the questions about keeping the hide flexible.
As for the jigs falling slower lets don't forget palmering a hackle feather on a light head. The ones I tied were on 1/64 and 1/80 and took a week to fall. Drove me nuts waiting for the line to straighten.