Not really any downsides.
The stock ignition is pretty weak and most people convert to 86-87 style.
Tranny is solid. Rear is solid. Motor is solid. Heads flow a little less than the 86-87's.
They will make good power, it just takes a little more parts and a little more money.
www.gnttype.org
www.turbobuick.com
www.turbobuicks.com
www.t6p.com