After 7 years, I don’t think it’s going to sell to this market.
Let’s face it, the odd Buick straight 8 isn’t exactly what most people are looking for. Not that it’s good or bad, just not a very big demand on a slow, heavy engine. If this were a Hemi or even dare I say a SBC, it would have probably already have sold. The hot rod style build dictates a V8 of some kind, not a low rpm torque monster from a luxury car. Not many folks around who have even seen a straight 8, much less worked on one. Split them, sell motor/transmission as a unit, rest as a rolling project.
Find another market. I don’t like Craigslist any more either, too many quacks and dope heads. Facebook Marketplace isn’t perfect, but it’s pretty easy to comb through and spot the scammers. Its audience is worldwide, so it will be seen. You have to be a member of FB to post on marketplace, but that doesn’t mean you have to post anything, although most people do check the profile of sellers, a little activity helps people know you’re not a scammer. I’ve bought and sold several things on marketplace.
Your call. Sit on it or list elsewhere.