The 480 (with the capability to enter airways by name, instead of loading in the whole list of intersections) is the only one on the list worth going for. The GNSx30 products are 1980s technology and my KLN94 + KMD550 is IMHO better.
But the install cost of a 480, in a plane in which it was never on the TC? £10k? One would need to rip up the whole stack and start again.