The problematic word in the subject of this thread is "simple".

An aluminum V8 auto-derived engine is not an aircraft engine - yet. It
needs a lot of engineering work to become one. If the engineering is well
done, the resulting aircraft engine will be successful. If it isn't.....
Many auto conversions weren't. It isn't easy.

Auto engines are high revving compared to direct drive aircraft engines so
to get a reasonable power to weight ratio, a PSRU is needed. But, isn't a
PSRU heavy? Yes, but so is the crankshaft of a direct drive engine - it has
to be to handle the torque. Auto engines have light cranks which are just
as strong on a HP to HP comparison since they rev higher. HP is just torque
(Ft Lbs) times RPM divided by 5252. Compare the weight of a direct drive
crank vs. the crank + PSRU weight of an auto conversion - not so much
difference as thought.

To minimize the re-engineering, keep the engine core working as nearly the
same as in a road vehicle but make sure it uses the best forged racing parts
like rods and pistons for durability. Use the lightest flywheel that allows
an even idle.

The PSRU is just a special PTO (Power Take Off) with gears. It mounts to
the flywheel housing and connects to the flywheel with a flex plate.
Millions of PTO's are in use as irrigation pumps so somebody knows how to do
it. It takes all the gyroscopic and thrust loads away from the crank which
'sees' no loads except torque. Make it from billet aluminum and use the
best bearing money can buy. I'd use a very close tolerance planetary
gearset for durability.

It will withstand high contineous power if you keep it cool. Design the
radiator for worst case cooling conditions and then control the airflow with
variable baffles. I'd feed a pair 12" diameter "barrel" radiators with jet
like wing root air intakes and rear fusalage exhaust . I'd augment the
radiator outflow with engine exhaust which keeps the radiator intakes from
ingesting hot engine exhaust while increasing airflow through the radiator.

I'd use 100PSI racing type fuel injection with in-tank pumps to prevent
vapor lock. I'd use closed loop mixture control with an O2 sensor. No
fussy carburator - no carb ice.

Would I put this thing in an airplane and fly it over the mountains at
night? Not at first - not by a long shot. I'd build it on a trailer so I
could run it in non-noise sensitive areas. I'd take it to air shows to
entertain but mainly I'd just run it on the trailer trying to break it. If
after a few years I still couldn't break it, then maybe in an airplane.
Ground testing is the expensive part. 2000 hours at 10GPH = 20,000 gallons
at $4 each = $80,000. Nobody said it was cheap.