If you tune the NAV radio to the ILS, switch on the autopilot and then press Ctrl-a to switch on approach mode, you can 'cheat' and get the Stratocruiser to follow the glide slope. Because of the relatively poor turning performance of the Strat, you can sometimes lose the ILS lock. It's therefore easier if you get setup on the glideslope and lined-up with the runway first.
Make sure the navigation radios are switched to NAV and not GPS. Ctrl-u toggles between the two on my system although I'm not 100% sure whether that is the default setting.
FYI you can also follow a GPS course if you switch the nav radios to GPS and then press Ctrl-n to follow the GPS course. I justify this to myself by saying that the navigator would do the hard work in the real world