Hello Mike; welcome to Torque Cars.
I have to admit that I'm not overly familiar with the Rover 414 you mention. If I'm right it has the K series engine (which is NOT Honda derived as the 416i engines were).
Yours is a twin cam unit - the Honda used a single camshaft to drive 16 valves in the 416 with a fairly intricate rocker arrangement.
I first drove a 214Si in 1989 at launch, which I think has the same engine as your 414SLi and it was an impressive piece of kit for the time and is still a worthy engine now. (If I've got the wrong car then please tell me ASAP
).
As far as tuning I have to admit I'm out of my depth with this one but I'm sure there's plenty of options available, and [plenty of] Torque Cars' members who will offer some practical advice.
Induction kits don't do all that much, in my opinion anyway. Others say differently so please do avail yourself of some proper input.
That aside, enjoy your stay, may it be a long and harmonious one.
Kind rgds,
Paul (HDi)