I thought now might be the time to replace both engines. .... Anyone have any experience with this big of a job in these boats?
Not personally, but the 300 I bought recently had both engines replaced before I bought it (mostly newl ongblocks with the accessories brought over) -- 1 due to age/hours and another due to an accident. It was pricey according to the receipts. I've replaced car engines myself but not boat engines, and when I was shopping for boats, for whatever reason it seemed like the ones I was finding either had very low hours on replacement engines, or very high hours on the original engines.