Rear-axle ratio and the 5-speed swap for highway cruising

With the common 3.92 (or earlier 4.08/4.27) rear axle and 4-speed, the Pagoda spins to around 3,000-4,000 rpm at highway speed, which owners describe as noisy and stressful for long cruises. The fixes discussed are transplanting a taller 3.27 rear from a 280SE/SEL 4.5 or fitting the very rare ZF 5-speed, both widely wished-for.