The Big Boy should have a Centipede tender, 5 fixed axles and a 2 axle truck on the front. It doesn’t have a Buckeye truck.
The standard 1.02” axle length with 42” wheels should work fine.
Mel
My Model Railroad
http://melvineperry.blogspot.com/
Bakersfield, California
I’m beginning to realize that aging is not for wimps.