110 Project

With the floor up the R380 serial number is much easier to read.

Its prefix is 68A with a suffix of L.

Which, I think, means its a long stick originally fitted to a Defender. This may guide future choices for an engine swap...some may be easier than others.
And no, the V8 (as much as I love em) is not on the list.

my compliments for the project! As an engine to have a simple thing you could use the BMW M51D25 of the P38, also mounted on the E39 525tds, using the gearbox bell of the P38 for the R380. This engine was born with an electronic FIP and an ECU, but you could eliminate them using the mechanical FIP of the 524tds. Of 4 cylinders without ecu the Toyota 1KZ, Nissan BD30 and TD27 (immortal with timing gears) are valid but you will need an adaptation flange