Bob Ballantine used to play on a tin whistle (possibly a Generation) that had had its mouthpiece removed and replaced by that of a platic descant recorder (probably an Aulos); it was excellent. His articulations were really crisp, suiting his Northumbrian repertoire really well. I gather he was a piccolo player originally and occasionally played a piccolo with its head piece replaced by a plastic descant recorder mouthpiece.
From all of this I got the impression that the mouthpiece was the critical bit, especially the fipple, when playing. Recorder fipples seem to have better quality control in their manufacture. The timbre, however, is controlled by the bore shape and the material in the body of the instrument.
Ian Simpson has a fine reputation as a maker of timber pennywhistles with fine timbre and playing characteristics. He can be contacted by writing (snail mail) to him at Nariel Creek, Victoria, Australia. He's the only Ian Simpson anywhere near there so such minimal details will get him. He also makes rather good anglo concertinas.