The engine has 250k on it. Needs new manifolds and a couple of seals.
Remember I'm in the UK. 5.0 was never sold here and my 97 is RHD
Si
That will be interesting, the RHD I have imagined trying to fit a 302 into a USPS Explorer based mail truck. They made one called an FFV which has a 1999 2nd gen Explorer SOHC chassis, 2WD or A4WD. The right hand exhaust manifold could be a major issue to fit the 302 into that RHD model. The steering shaft is very close to the engine and the 5.0 explorer has a unique OEM manifold made to work with the shaft on the left side. You might be able to take some measurements of your RHD truck around the steering shaft, to try to figure out if it will clear using the 5.0 manifold in your truck.
I'm sure you can find an engine machine shop there who can work on the V8 heads, they are very easy to work with. The engine might be fine to use as is with that mileage, depending on the prior care as I said. The heads are fairly easy to R&R to have refurbished like I suggested, when the engine is out. The cost should be about $75 for the head gaskets, $150 or so for a quality valve spring kit, plus the labor to install new valve guides and the rest. Replace the injectors also if they are an unknown age.
You can probably also use the old cat pipes if they haven't been hurt by anything chemically. I don't know your emissions laws, but there are decent universal cats which can work for under $100 each(only two are needed, strict emissions laws like CA require four high dollar units).
All three of my 302 Explorers have about 225k miles on them, and one will be a project truck that I will refresh the engine for a short term reuse(new engine much later). I'll rebuild the heads and install new front and rear main seals, water pump etc. If the core engine is okay(the cylinder walls not worn badly), the engine can last a bunch of years to come. But the valve springs and guides get worn out by this age, they need help if it's possible to do it.
For the engine wiring, with that 98 harness, Jamie can help with the minor changes to make to it. The 1996/97 system used slightly different wiring in that engine harness, just a few wires, versus the 1998 and 99-01 systems. Don't let that worry you, but be concerned about the handling of the wiring a lot, both removing the engine and the wiring while doing the swap. That wiring is very fragile at this age, you don't want to create any breaks inside the wiring looms, which can be trouble later. The injector connectors will likely break, but those can be replaced easily.