Can the push tubes be removed with the engine in the car?
Is there enough clearance?
Brian

Yes...

Yes, but in a couple of cases they can only come half-way out. That's OK, though, as you can reach both ends of the tube while the tube is hanging from the hole in the cylinder head.

--DD

You can def replace them with the engine in the car, but you’ll have to be extra thorough in cleaning the bores since you won’t be able to see all angles. If the PO used sealant and that’s the cause of the leaks, it may be too difficult to get the old stuff out without more access.