I thought you would say that. Cheap engines are not a good start to an engine swap. Castlemaine Rod Shop is the old man of engine and gearbox adapters and has a Cleveland V8 to landcruiser gearbox adapter. You would need to make sure its a H55F gearbox and not an R151 but adding a v8 to a R151 would be a terrible deed.
You asked if anyone has done it before, well yeah, but no one ever seems to want to do another one and the resale value is dismal.
The 73 series is fast becoming a desirable landcruiser and keeping it all Toyota is what I would recommend, especially if the interior and body are good..