The 3B is an indirect injection diesel and really needs glow plugs to start. The relays are mounted to the bulkhead of the original vehicle. Therefore, they are likely to original to the 3B engine.
The 13B is a direct injection engine with no glow plugs. It has a glow screen intake heater, but being direct injection, the engine will happily start without these unless it is well below freezing. Therefore, many people don't bother connecting the glow screens when doing direct injection engine swaps.
Unless the relays are obviously user installed (generic parts screwed on with self-tapping screws etc), you can be pretty sure that they are original to the vehicle, and therefore the 3B. Why not wipe some of the dirt off them and see if they are original Denso relays?