Not so quick

the Dura Ace 7402 RD could work. But you need Dura Ace 74xx shifters to make it work and a compatible freewheel/casette (not sure what you have there, but it looks like a 6sp and I would bet that it is not compatible). The 7402 is really build for an 8 sp Hyperglide set up, but can do 6-8 sp in either a Hyperglide or a Uniglide set up. No such a thing as a 6 sp Hyperglide, so looking for a 7sp Sante/Tricolor/105 Uniglide freewheel might be in the OPs future...