New a-body owner

Hi guys I have resently purchased a 67 valiant 2 door post, this is a solid little car. I have went over it from top to bottom and found almost no rust. The car is all original, and was a one owner. Only 88000 miles. It has a slant 6 with auto trans and small 7.25 rear. I want to change to 360ci motor and 727 trans and 8.75 rear, but Im finding out this is not so easy. I am having trouble finding parts for interior/ exterior ect. I would love any ideals or advice.