They come both ways, tiller is more common though, depending on the make model and year it can be easy and cheap to convert, or expensive and difficult.
I know from experience that the small mercs from the late 70's and 80's simply use a bracket bolted tp the bottom of the tiller mount. Cables come in under the cowl and attach to the shifter and throttle linkage Bracket is NLA new, however there is eBay.
