............ as well as the massive ventral fin (don't over rotate on take-off):
That was fitted at the behest ( demand ? ) of the British ARB when the 707-436 was presented for UK registration. (also I believe the second hydraulic rudder boost system, the switch was fitted as an afterthought on the edge of the F/E's panel -but don't quote me, a long time ago now ! )
The early PanAm 707's didn't have that ventral fin, and I recall a PanAm pilot thanking us one day in New York Customs Hall as we awaited our bags. He reckoned each take off was a breath holding cheap thrill, there being a speed range at which, should an engine quit on take-off, there was insufficient rudder control and authority to keep it straight and on the runway until the larger, ventral, surface and added hydraulic assistance was fitted.
I think that there was the occasional tail scrape, can't quote, never happened to me.
just sayin'