In my scone its no surprise if an "A" can make that power
considering an inferior similar pushrod 1.4 litre can make
500hp in rally racing spec with massive boost.
That dont "Sierra" in developed Renault R5 GTs have smaller
valves and ports than an A series but otherwise looks like
a twin, yet has amazing manifolding / hardware and I dont
think wet sleeves help it to be stronger than an A series
as some forums report movement issues at high boost.
50PSi assures a grenade, they take it for short periods.
The solid little A series could make big power if setup
properly and reliably providing cooling and pre-ignition is
not & issue but like you said few have the money, time or
inclination for big hp when also there are other options.
Shoot out mode on a DD is not considered the most reliable
hp reading as its always on the high side and humans love
to brag over big things no matter the activity.
If you look at the curve on the screen its very peaky and
would not be easy to get to hook up on the track without
some major chassis/box settings and driving skill etc.

The T50 does not have the best first gear ratio so its
an achievement to run that fast if its a stocky t50.
Im sure theres a bit more to come from this car yet hitting
the 9s will be easier in a well setup auto.

I dont believe any 8v L series has run this fast :)