Overland Diesel swapped a VW diesel into a Jeep CJ3b. They made a custom adapter to fit the engine to the T90 transmission.
Acme adapters makes an adapter kit for a VW to a Suzuki or Toyota drivetrain, so that may be an option.
IMHO, I think the 6.2 or 6.5 is suited for a Wrangler, and most of the small block adapter kits will work with the 6.2 & 6.5s. If you gear it right and keep your foot out of it you should be able to get at least 25 mpg.
1993 K3500 - Peninsular 18:1 engine, marine injectors, high capacity cooling, AL Core Radiator, 3" DP and 4" exhaust, ISSPRO Gauges, Girdle, AMSOIL Dual Oil Filter System, 1997 Air Filter(trashed the K&N), 395K on Body, 165k on engine.
1997 GMC Savana - 6.5 TD
1966 CJ5 - V6 Gas - highly modified
1967 Jeepster - Stock
1986 Jeep CJ7 - Stock
1993 Grand Cherokee - 6.2 diesel
2007 Grand Cherokee - 3.0 diesel