Technically no you don't have to apply the factors to the QRH because the performance is intended to be used in flight, ie after dispatch. The despatch rules do not apply in flight.
Perhaps a very simplistically dangerous philosophy ?
In the situation of an abnormal or emergency, the pilot appropriately needs to have a reasonable set of data available for his/her assessment in resolving the recovery. Indeed, it may be necessary (and appropriate, on occasion) for the recovery to involve reduced margins when compared to the normal certification approach.
Keeping in mind that the distance factors are built in to provide a reasonable probability of successfully completing the flight, it is more appropriate for the pilot to
(a) assess all reasonable options
(b) rank the options according to whatever criteria are pertinent to the particular situation
(c) adopt the most appropriate solution for recovery
In respect of landing distance factors, this might come down to comparing multiple available runways .. one should have a good risk-mitigating reason for deciding to use a runway with a significantly lesser factor. If, of course, there is only one runway available then that part of the solution risk assessment can be bypassed ...
The philosophy can be carried across to considerations of any post launch defect situation .. assess and rank the options prior to making the call. One of the resources you have is the MEL .. if you have time to review the MEL, and you choose not to, then I would prefer NOT to be in your shoes at the eventual enquiry if the recovery turns pear-shaped.
The 1.67 factor applies to heavy aircraft scheduled performance while 1.43 normally is for alternate aerodromes if the particular rules permit the distinction.