I have MBS (Japan) bearings in my 54 3600. On a first impression, they are quite beefy and well made. When it comes to fitment, they were very tight. I had to use quite a bit of emery cloth on the hubs to get the races to go in. The spindle, same story. Lots of emery to get them to slide on.
The OE felt seal woudn't work on the bearings either. I had to cross reference a rubber lip seal. I couldn't drive the seal in all the way, or it would get into the bearing.
I also had to use a bushing between the inner bearing and spindle because there was too much end play, the hub wouldn't seat all the way.
Now, I know, I have a 60 year old truck, so I'm sure the spindles could've been slighty out of round and there is no telling what has been done to the truck over the years.
They seem to be good quality products, but need a little improving. I'm sure I'll get years of service out of them.
On the flipside, If I had to do it all over again, I would stick with the original ball bearings. With the modern high temp greases, they are more than up to the task.
These vendors have tapered and ball bearings availible
http://www.classictruck.com/
https://www.chevsofthe40s.com/