"Whippy" refers to frame flex particularly around the bottom bracket during hard acceleration/climbing. If the chain grinds against the front derailleur when you stand up you're getting some of that flex.

I'm not a big fan of Simplex shifters and feel a switch to 1970s SunTour would be an improvement. Some will agree with me, some won't.

I have a question for the Lambert experts out here: Unless my eyes are fooling me that bike does not have the pressed in BB, I'm pretty sure I see a threaded lockring. I'm familiar with the marque in its Viscount form, did earlier Lamberts have conventional BBs? It's been mentioned that Braxton was a builder. Perhaps he threaded the BB shells for his customers he knew would be touring and might need a BB serviced at a shop that didn't deal with the relatively obscure Lambert?

Thoughts?