Missing the items you listed, the seller is off his rocker thinking he can get $120 for it.
Things like missing the vanes and such knock the price down a lot. I'd say the WHALE itself would be worth $25 alone, maybe $30 if you are feeling generous.
I rebuilt a considerable amount of my own WHALE, slowly over time, and it's not yet complete, but I wouldn't ask more than $50 were I to sell it.
Mine is displayable, with all the things that offering is missing, save the vane assemblies. For about $30 you can find most of those missing parts anyways.
I think your offer of $50 for the lot is plenty generous, and if the seller declines or is offended by it.....don't sweat it. There will be other, better offerings out there.