Jim, I just got my Oliver 1650 a month ago and I wondered about the shift pattern too. Just feel how the gears pattern with out the motor running. Its easy, you have the pattern right in front of you. As long as you have some room to manuever, just start off and try it. I'm still real slow in shifting, but I can basically go through all the gears okay.
You mentioned the over/under shift. I think some Oliver models have both over and under drive in addition to direct drive (actually 3 ranges).
My 1650 has two ranges, the Hydradrive which is an under drive (or lower range)and Direct Drive which is the higher range. You don't have to use the clutch to use it. Just pull it out for lower range and push it in for direct drive (higher range). An easy way to shigt without the clutch.
Be sure to use DIRECT DRIVE if going down a hill as the drive is free wheeling so to speak, that is the engine will not brake you. Personally, I drive mostly in Direct Drive for now while I'm trying to get more comfortable with the shift pattern. Ed