The turbos are pretty tiny and probably don't add a lot of pressure to the manifold. You could probably install a manual boost gauge if you wanted to. A modern pickup truck diesel (Ford 6.7, RAM / Cummins 6.7, GM 6.6 Duramax) can produce around 30psi of manifold pressure on top of atmospheric pressure (14.7 at see level). A Ford 3.5L EcoBoost, such as found in the F-150, produces about half of that and uses smaller turbos. On the Kubota, the turbo is again half the size of the Ford EcoBoost turbo. I'd say its producing less than 10 psi of added pressure. Its also worth noting there is no intercooler on these engines, so the compressed air is hotter.
Kubota makes several versions of the V-2403 engine. All are 2.4 liters common-rail, directed injected diesels, but some are naturally aspirated and others are turbocharged. Of the turbo models, there are different power ratings. Presumably, the added power is via additional turbo boost and the added fuel to make that worthwhile.