what size is the engine

The engine sizes available in 1971 Caprice were 350, 400, and 454 cubic inch. A 1986 most likely has a 305, which will fit with some adaptation, but the bigger issue will be the emission control items, which were different by 1986, and may cause fitment or running issues. I'd try to find a 350 from an older vehicle to put into the 71, myself. These are plentiful.

you can remove the emisson control if need be i dod on my car it doesnt affect anything and u gain alil power but it wont pass inspection if u have to go through it

can a Chevy Caprice SS motor fit in a 2008 Chevy Caprice LT

Ss motor fit in a 2008 caprice LT

what size engine in caprice 1989