I don't think Sunn ever used JBL 18's. They'd gone to proprietary drivers (transducers) before they used 18's. The exception was the Cerwin-Vega 18, used in the 118V and the 118VH (that's what the V stands for).
I think that the cabinets came in two configurations, top and bottom. Not much difference between them other than looks. They function the same, but the cabinets were designed so that the jack and nameplate were on the top end of the back of the cabinet, whether the vent was above or the below of the driver.