I would almost certainly screw up trying to do that.

I don't see how. Assuming your 430s have a flight plan and you're following
it, all you've got to do is engage GPSS and ALT. Or GPSS and VS and then
dial in the vertical speed you want on the autopilot.

You know, the A/P in my Twin Comanche can do wing level, heading hold,
and it can sort of track the LORAN but I don't like how it does that -
too much hunting. I put it in because I got it cheap. Altitude hold
would be nice, but installingthe pitch servo is a pain so I don't have
it. For years, I flew the plane night and hard IFR with no autopilot
at all. I still don't use it in IMC - it's for long boring stretches
of VFR flight.

I have actually flown planes that had GPSS, VS, and similar funtions.
GPSS is great when you know exactly how to engage it. I once borrowed
a Mooney that had an STEC and GNS430 with GPSS. Took me about 15
minutes to figure out why it wasn't working - silly me, I thought
following a GPS meant the A/P should be in nav mode. Nope, heading.
Honestly, if the weather had gone foul then, I would have disconnedcted
the silly thing and hand flown it instead of figuring in out.

I used to instruct a student in an Ovation that had the KFC autopilot.
Had to learn how to work it to explain it to him. He kept busting
through altitudes with that VS function. Turned out the solution was
to press one more button - and then it would say ARM and that meant
that when it reached the altitude preset it would level off. I'm not
sure I remember how to do it now.

Anyway, my point is that without the manual, I would likely not be able
to figure out how to press all the buttons to correctly couple up the
autopilot to the 430 for an approach. I'd get something wrong, for
sure. And all the button-pushing would distract me from doing my job -
that is, landing the damn airplane. And I can assure you that with a
moving map GPS, an AI, an ASI and an altimeter I can fly an approach
and land the plane - it's nothing compared to doing a partial panel VOR
with just a TC and compass, never mind an NDB.

Michael