spirit of 76

I was looking through the local ads and found this 1976 spirit of 76 Dodge Dart lite spirit of 76 car,the body is rock solid and still has all the original parst like the hood and trunk lid the bumper braces and the 3spd with o/d the original seats still in place but need some help.I have the original motor but it needs to be rebuilt,I have all the documentation to back up what this car is,my question is,does anyone have any idea how many Dodge dart lite spirit cars were made?I found info that told me that there were just under 1000 lite cars made but how many spirit of 76 dart lites were made,I know it would be a guess but how many may remain?and should I change the k frame and go BIG BLOCK,or rebuild the 6