Thanks for the research but what they are referring to are solid state flashers (not typical flashers used with incandescent bulbs) which are the ones I purchased from Chev's40's. Their use is not limited to switchbacks but all LED's.

Without them, the LED's didn't even flinch (knew they wouldn't, just wanted to see what they did while waiting on the right parts).

'69 1/2T stepside, Sea Foam Green, 250 L6 w/ 3 on the tree, not an option on it, in the family since new.