I'll nominate my own 68 K20 with a V6 Toroflow Diesel as the largest six banger here.
Specs: 1973 478ci GMC "Toroflow" Diesel V6 hooked to a nonsynchro 5 speed and a divorced Spicer 23. Axles are D44 and D60. Factory air, full gauges, custom interior, approx. 4" lift on 35x12.5s.
Looks rough, but is my daily driver now that my 67 Chevelle has sold.