@dr.power,
at what frequency you need to use this phase shift generator?
if the frequency is Higher than 8 or 10MHz, i fear 40xx series wont be suitable and you have to resort to 74HC or 74AC versions,
Phil Ric's SDR TX appears interesting and you can clearly see that he used 74AC 74.
in the front end also, i suggest to use 74HC instead of 74LSxx
@Nigel Goodwin,
perhaps after all the modulation \ quadrature mixing is over , one can have a filter to remove harmonics, and the SDR designs of Transmitters are not uncommon now a days. However, I am not a HAM licensee , though I worked in RF field in Indian telecom scenario.