At ISA sea level the J.31 needs 1,440 metres at MTOW.
For ISA sea level +20C the J.31 needs 1,650 metres at MTOW.
For ISA 5,000ft altitude +20C the J.31 needs 1,830 metres at MTOW.
Hmm rather take a J.41 thanks, but less humorously I'd still like the real figures and not speculative thanks...