Replaced the standard, 125,000km vintage valve with an N75J from the dealership (they didn't know what it was worth, got it for about the same price as the standard part).
Took 5 minutes, no 'idiot rashes', scratches, scrapes, all clipped into the position of the standard part.
Impressions; initially, didn't notice any difference. Second gear... OK, feeling slightly better. With moderate pressure of the accelerator 3rd gear felt like it was much improved. 4th even more so. 5th... Well, you get the pattern.
For the same amount of acceleration required noticeably less peddle. And kept pulling higher through the rev range.
Unsure what condition the original valve was in, and whether the differences are due to being better, or more serviceable; either way happy camper.