The 3.1 V6 is a 60 degrees-between-the-cylinder-banks motor derived from GM’s X-car engine of 2.8 liters. The 3800 V6 is a 90 degree cylinder angle motor derived from a 60’s era V8 later sold to British Leyland and used in lots of Brit cars. They also offered a 3.4 liter version that seemed noisy and rough for no reason. All are cam-in-block with pushrods with 2 valves per cylinder. Nothing fancy, proven technology.
The 3.1 was a pretty good motor as long as you fixed the intake gasket before any harm is done. Smooth with reasonable power. It will run a long time as other posters here have said. I’ve got a buddy who raced Berretta’s in the local circle track “compact” class for FWD small cars. His race cars used un-touched engines with well over 100,000 miles. Never had an engine fail.