Thanks to all the help here, nearly figured this conversion out. Will use a new Shimano 7 spd freewheel with washer if needed and a new SRAM or Shimano chain. Last issue is the downtube shifters, To double check: found a pair of NOS 7 speed shifters on Ebay. Ad says they don't have bolts etc. I should be able to use the bolts etc from my 6 speed SIS, correct?

Shimano Light Action SL A500 7 s Downtube Shifters New Indexed or Friction | eBay