Some forks from a 2001 mountain bike (26" wheels) are now fitted. The original Peugeot forks are slightly narrower, the chrome lock nuts, brake cable holder and quick-release clamp do not quite fit over the new forks. Maybe the new one is 1" = 25.4mm, the Peugeot 25mm? There is not much in it, I think some filing could help things along. I don't think enough of the new forks hangs out at the top to allow the quick-release clamp to be fitted anyway. The bearings did not quite co-operate either, I used the new ones at the bottom, the old ones at the top. Let's wait and see how it goes. The new forks are about 2", 50mm longer than the old ones. A mountain bike wheel has a rim diameter of 559mm, vs 490mm for the original 550A wheel. (559-490)/2 = 34.5mm greater radius. So the front of the bike should be lifted about 85mm.
I'm thinking to move the seat clamp to the front of the pole, to move the seat forward if it is too far back with the new wheel.
I might try removing the chrome bearing housings and using the ones from the mountain bike (at another address right now). I will measure the head tubes to see if there is any chance of them being the same, but I guess it's unlikely that this would work. It is possible the chrome thing at the bottom may deform. I think I'll just give it a go and see what happens.