I have a 1967 Dart GT. When I purchased the guy gave me 2 extra motors as it was his last A body. One is a 1981 Slant 6 out of a Dodge truck, cant confirm the block casting as it is laying on that particular side. What appears to be a 1968-1970 Slant 6 (2806830-6) with 5 freeze plugs. A 1966-1967? (2463430-25) Slant 6 with 3 freeze plugs that is currently in the car. If I were to focus on one of the motors to do a complete rebuild and do minor HP upgrades (cam, super 6, HEI) which would be best?