I played the Vito neck on the Vito and then on the 25 (once I'd sorted the octave key issue - post #41 above) and they sounded the same, with that warmth I associate with the Vito.
Can't play the 25 neck on the Vito as won't fit.
Played Vito neck on the Vito and the Yam neck on the 25......sounded almost the same but again the Vito was a shade 'warmer'.
The necks look identical and measured the same from pip to either end etc. but the Vito neck is approx 3-4g heavier so perhaps a slightly smaller bore? Would that account for any difference I hear?
The weight of the crook won't make a difference - it's all in the very boring internal dimensions.
If you're not convinced, slap a large ball of Blu-Tack on the crook and see what happens.
I've done many, many hundreds of setup jobs on batches of 'identical' horns - and if you had ten such horns and played them one after the other you'd have two, maybe three or four, 'outliers' that were either noticeably brighter or warmer than the rest of the sample...with the rest being more or less similar but with subtle differences.
And then you can have lots of fun swapping round the crooks.
It's a bit like those classic western movies where the gunslinger makes a gun out of this barrel and that cylinder etc.
Anyway, glad you managed to get the test setup working. As you found out, the crook makes a LOT of difference - but there'll be differences in the dimensions of the horns too, which'll temper the tone somewhat.
If it comes down to it and you find you really want to put the 25 crook on the Vito, it can be adjusted to fit...and then re-adjusted to fit the 25 again.
Another test that's worth doing is standing the crooks side-by-side (tenon sleeve sitting on the table) and comparing the angle of the crook tips. Lots of players miss this little trick - and the 'approach angle' of the mouthpiece can make difference in the way the horn plays.