Confusing
You all are forgiven, its confusing. You almost have to say IO-360: 180hp/200hp or parallel-valve/angle-valve. The suffix is mostly good for knowing what kind of crank it has (counterweight or not) and magnetos.
The confusion is a O-360-A1A is 180HP/parallel and the IO-360-A1A is 200hp/angle valve.
Some people think (I know) that the fuel injection alone makes a 180HP a 200HP engine and that they are similar engines. According to Lycoing they are totally different engines, for all intents and purposes, and there's few interchangeable parts, apples and kumquat's. To make it worse Continental makes an IO-360.
Lycoming:
"The IO-360-AlA features a horizontalfront-mounted
fuel injector, angle valves, 8.7:1 compression ratio,
and is rated at 200 HP. The IO-360-A1A incorporates
additional design items which are not included in the
O-360: piston cooling nozzles, stronger crankshaft,
tongue and groove connecting rods with stretch bolts,
tuned intake system and rotator type intake valves.
There are actually few similarities except for the
360-cubic inch displacement."