"An 87 150 Magnum was a pretty
"An 87 150 Magnum was a pretty decent motor and a good candidate for a rebuild (in most cases).
You have consider all your options...
You can buy a new 150 for 12-15 thousand bucks and it will have a life expectancy of say 8-12 years average before it needs a rebuild (but it could last 20 or more years without issue).
You can buy another used motor from "some guy" that is selling a motor that is "so perfect" that he wants to get rid of it, and inherit whatever is wrong with it.
You can rebuild this one. If you get a shop to do it, powerhead rebuild and carbs will run you upwards of about 3500 bucks at the top end (depending on exactly what needs to be done/replaced), or if you have the ability, you can rebuild yourself (using the services of a shop for things like boring etc).
The "self-help" rebuild could be done on this motor for maybe 1500 bucks.
In any event the rebuild may last you 8-12 years on average (or like a new motor, which it practically would be, you could see 20 years of trouble free service)..
The choice is yours..."