I/O Conversion

New to the V20 site. Own a 1985 v20 with original 170 mercruiser. Purchased from original owner 4 years ago. Still runs well but want to convert to outboard at some point. The expense of keeping the old I/O going seems to be about $500 to $1,000 per year. Always some problem. My local shop doesn't like the idea. Balance issues, expense etc. Thinks I should put a new mercruiser MPI 220 hp in. Any thoughts or experience with a conversion.