Well after more or less completely taking the engine to bits, my dad and I have fixed the XR2. We replaced the camshaft and tappets, bead blasted the cylinder head, ground down the valves, cleaned them with petrol, and polished them, it's running on all 4 again. Then it failed its MOT. Had to get the tie bar bushes replaced before it would pass, then fix the radiator fan so it could do an emissions test (which it sailed through). And now, after being in the garage since October, and £630 later for fresh insurance, its back on the road and my daily driver once more.