Think I remember reading that the very early M70's (pre WWII) are not the best for custom guns, that the later, but still pre-64, guns had some improvements that make them more desirable. True?

There's a very early gun, 1937 first year for sale near me that's had the rear ring D&T'd so it has no collector value, thinking of parting it out for the action if it's worth it.

Sure, How much ? $200?

Depends on what the stock & barrel bring, probably wants $600 for the whole rig.

I have an 06 custom on an early Mdl 70. Only real disadvantage is the safety is on the left side of the cocking piece and works backward more or less. Slightly awkward to reach but has not stopped me from using it in Africa as one of my favorites. I know of no other disadvantages to them. I like it much better than the trasition with the little skinny safety lever. You used to be able to get what was called a 'Tilden' safety for them that moved the safety to the other side but don't think they are available any more. Have never tried it but think a later model cocking piece would exchange with little effort.

Jim Wisner has a retrofit to convert the safety..pre war M-70's are VERY desireable

I cannot find the safety currently listed at Wisners. I thought he still had some in stock.