Are girdles generally added for big rpm or HP or torque

It is worth the cost to check. How well balanced the kits are I don’t know. Perhaps passable for no vibration is what there doing. Which is different than a race assembly which should be down as close as humanly possible. An assembly can be 3,4 or more grams out of wack and you won’t feel it. OE balance jobs can be worse. If he can get it a better balance, then by all means, do it.

Is the 360 more prone because the journal is larger? I don’t know. Is the cap smaller, thinner?
I’d have to check.

And yea, no worries. Don’t feel bad. When I read your question, I was like, “OH yea it’s.. oh ****, it’s ummmm, it is... crud! Where’s my book damm it!”
Yea, I had failed the pop quiz and looked it up.
It happens!