These shifters are part of one of the Exage groups from the late 80s.  Not sure exactly which one (or maybe more than one variation of the line).

NOTE: There has been some speculation on if these shifters are 6sp or 7sp.  All references that I can find online about this model of shifter indicates that it is a 6sp SIS shifter, however I have had reports from actual owners who have both claimed to have 7sp and 6sp versions of this shifter.  A quick web search turned up several eBay auctions for these shifters with a clearly visible 7S on the side of the black ring which proves that there were 7speed versions of these produced.  Be aware of what you need and what you are buying.

Addendum: There is a mis-strike on the part number cast into the underside of some left levers. The numbers looks like SL-8434 or 8L-8434 instead of SL-S434. Ive seen these incorrect numbers quite often on the internet. See the last 2 pictures that I posted of the part numbers

SL = Shift Lever. The letter "A" or "S" before the numbers usually indicated the lower priced models from the economy groups.