6A12 good points - Compact (fits in the same space as a similar capacity 4 pot), fairly light (lighter than my 3SGTE was
), already makes 180hp out of the box and gaining 20 hp is very easy, they respond well to simple mods. They also sound bloody nice, though most small capacity V6's always do.
Downsides - Fairly rare, and hence not a lot of off the shelf aftermarket gear for them, depends on what you really want though. RPW in oz make a lot for them, but you pay through the nose for it.
In oz they are a reasonably common swap for the mivec mirages, its literally a straight bolt in swap - I have no idea what you're planning on putting this into though! The fact its' designed to be a high - revving screamer in a performance-ish application is a good thing, as opposed to taking a normal shopping cart engine then pushing it. Same as starting with a B18C-R instead of a B16A really.
The mazda/ford engines are also a good option - I've heard of some great results from them, I think the radisich ones make 200hpish from factory? Try getting hold of the guy who does the datadots in wellington, he's on a couple of forums as "FPV270" or something, he knows his stuff on them.
Just my 2c anyway. Curious to see whats going to become of this!