New piston rings a job that can be done in the car ???

[LandRoverGhost]

While it, in theory, CAN be done without removing the engine from vehicle, that will make it infinitely harder, especially with mobility issues. If you were local I'd volunteer my neighbour's garage...but it's a bit of a swim for ya!

Low compression may not be rings, but 30psi difference between cylinders is cause for concern... What thickness head gasket? Did the block/head get decked/skimmed at all? A leak-down test will tell you more. Did the head bolts get done up in order?

The cross-hatching is only to wear the rings into the bore...smooth bores are fine. If that's what you're thinking.

Since the camshaft comes out the top...your call whether you replace it, unlikely it really needs it and more likely worn items are valves/ valve guides/ springs, maybe cam journal bearing shells.

If you're taking the engine out though, it would pay to flip it and do main (crank shaft) bearings, That'd give you peace of mind for the next 400 km

Thanks - new valves in the new head should all be OK , so look at bottom of engine now.
Cheers:
j.