Since the topic really comes down to a naming issue, there's two parts of it as I see it.
The factory docs are pretty clear (except for Nov 68) - L74 is referred to as an H/O.
But as an outsider, I'd never heard of an 400 H/O. Only RAIII and RAIV. So it appears that the hobby considers the L74 engine to be an RAIII. The big qualifier is that - what ever you want to call it, to be a true R/A car, it also has to have T42/611. You can have a R/A engine, but not have R/A.
