86 to 88 420 sel engine swap
 

will an 86 420 sel engine match up to an 88 420 sel car?

yes.

just got confirmation on my motor, 12 days and i'm on the road.thanks for the good advice. james

Are you legal?
 

Just a side note, that in some states (such as California) there might be an issue with an older model year motor in a newer model year car.

On the theory that the older motor might have LESS emissions control equipment than on the newer car had on its motor. IE, all 1988 cars must have ALL 1988 smog equipment on them.

I'd just check it to be sure I was running "legal" in my state if I were you.
You could be perfectly fine -- or not. Depends on the state.