OK465:
Apart from altitude issues....
I would guess that for RNAV equipment, a 'vintage' Be1900 would probably be equipped with a G530 or even 430, a fairly basic display of the profile, IIRC without displayed altitude constraint info.
In addition, when holding using this type of system, the steering guidance for NAV goes into a 'suspend' mode at the intended holding fix, requiring use of a HEADING SELECT type mode for the outbound leg of the holding pattern AND the turn inbound. So you're not really on a structured RNAV routing at this point. This is holding 101.
This requirement coupled with the existing 17 knots or more of right cross outbound at holding speeds probably ~150 certainly makes precision tracking as well as positional awareness challenging.
No doubt that holding with 400/500 is quite a challenge, having to use OBS mode and such. And, "suspend" for a HILPT is only good for one circuit, then OBS holding would be required.
Same for a 400W/500W although they supposedly get course guidance the first time around. In any case the evaluated and protected airspace for this hold is huge, because it was evaluated for climb-in-hold (310 KIAS) for the missed approach for the RNAV Rwy 1.
The terrain they hit is well within the 200 KIAS primary holding area.