Unless they used a VN750 on the dyno, then it isn't directly applicable...
The suggestions of 140/40 to 142/42 with 1 or 2 shims is a well tested combo that has proven results. There are threads with dyno tests if that's what you need to be happy with the general consensus on the matter. Check out threads by lance328 as he was really on top of the jetting for this particular bike's setup. If you view his old threads, people would post their setup and he'd provide the appropriate jets. They ranged from stock to 142/42 2 shims. Yes, lance did derive these from actual dyno tests to my understanding.
And really, on top of all that, my spark plugs' color doesn't lie. At least for sea level, 142/42 2 shims w/ ear shave and V&H cruizers leave my plugs a perfect color.
1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
Duralast Gold ETX15 AGM Battery
Coastered & Shaved
Metzeler ME880 [110/90-19, 170/80-15]
Balance Dampers Replaced
Rebuilt Forks w/ Progressive Springs
VN750.com Grill Cover
Emgo 23-92411 Handlebars
MOSFET FH012AA R/R
1990 Kawasaki Vulcan 750
1998 Honda VFR800 FI
2014 Honda VFR800F
1989 Pontiac Firebird Formula 350