What Axel said.
Been there and done that. Idles like a big block but sounds airplane-ish on plane. Most that don't know what it is seem to like it. I'd do it again. Some would not.
The cheap way costs about $250 in parts. All you need are tips and hose. You can plug the y-pipe. You can always convert it to silent choice later by adding diverters. I added silent choice after the fact to my X-18 with a 383 later. It was not a big deal either.
If you have an OMC drive (I don't remember the exact end of that era), you will have to modify one of the tips to get around the steering.
2001 35 Fountain Lightning w500 EFI's
1973 X-18 - Merc 383 Magnum
1974 Chris Craft Roamer with 1271 TI's