1800cc or 109ci engine suggestions??

[jim]

Hi guys, been floating around the forum for a while, loads of great info!!
i am hoping you can offer some suggestions for a suitable outboard to suit my new to me 15 foot hull. The rules here in australia allow for upto 1800ci or around 109ci maximum for this size hull.
Its a pad vee bottom and is very light (i can lift the transom end from the trailer quite easily), i will be doing mostly long river races but also some club days circuit racing, mods to engine are basically free, just needs to run a shifting case as i understand it.
I know an inline six is a good option, but i would like to know if there are any other good options?
i've only played with v6 mercs but keen to try new stuff!
Cheers, Jim