Is it so hard to realize that the 120r is a Harley engine, not a Jim's?
Some facts,
The Jim's 120 has;
Bore x Stroke 4.125" x 4.500"
Jim's own cyl stud spacing, and therefore their own cyl heads and cylinders.
Has Jim's their own crank case??
The 120r Harley engine has;
Bore x Stroke 4.060" x 4.625"
Standard crankcase and stud spacing.
If the 120r is reliable or not remains to be seen.
But to dismiss the 120r just because a different manufacturer has (had)
some problems with an engine of the same swept volume is plain wrong.
edit,
Sorry for repeating the facts Deweysheads, you beat me to it.
And the 120r comes with 10,5-1 pistons according to the SE catalogue.