being someone who builds and messes with other converted vehicles frequently, again IMO it really depends on who did the conversion and the quality of the work etc etc. I have walked up to conversions and been able to figure things out right away, in some cases easier than if it were the stock motor. But both sides of the coin, I have seen some amazingly poor quality swaps too.
Again it really depends on the vehicle and your mechanical ability or it you have money to spend it you are paying a mechanic. If you have little/no mechanical experience then you all are correct and I might shy away. For example near any swap by Proffitt's Cruisers I would trust and purchase and work on any day of the week. Even if it were a complex EFI system. Even though even they get some little things wrong here and there, they are still high quality, easy to follow, and easy to repair. But again I have seen nightmares too. Also much of it depends on the complexity of the engine and other components as well. For what its worth...
Again in the case of this vehicle, the price and original mileage of the truck dictate that it is more on the homebrew side of things. But if I were able to inspect it personally and see how things were done, I might not hesitate to purchase it at all.