Welcome man, I don't know about helping you diagnose your vibrations, but I will rip on your new engine in a cruiser for you
Does it only happen between the speeds listed or does it do it at other speeds as well?
My rig... "Maude"
1976 FJ40 with some stuff and some leaks.
1999 UZJ 100 Series bone stock ready to rock AKA:The backup minivan
2012 Toyota Sienna Minivan, fastest Toyota in the stable.
My camping trailer build up thread.
"You 80 guys are just a Sawzall away from nirvana." -Red Chili