'Flapless' in the VC0 does not imply that the aircraft was also slatless!
IIRC, Vat flapless is around 20-25 KIAS faster than normal Vat (depends on the mark of aeroplane). The performance calcs. and regs. for take-off, ferry and landing are very straightforward and rarely limiting.
Flapless and slatless would be a full emergency. Something like 40KIAS above normal Vat - and would most likely be the result of a total hydraulic failure which would also mean no TPI trimming, no speedbrakes/spoilers, no nosewheel steering - and little if any braking apart from accumulator and reverse thrust. Never practised in the aeroplane - and not even taught in the simulator on the course. Quite tricky to fly even in the simulator and you need the longest RW you can find. Which is why it's worth knowing where the longets RWs in Europe are - LHR and FRA.