Will a 302 bolt to bell housing and 3 speed trans in place of the 289 66 mustang?
Yes, a 289 and a 302 Ford small-block V8 share the same bellhousing bolt pattern. Therefore, the 302 will bolt to the same bellhousing and 3-speed transmission that your 289 currently uses in your '66 Mustang. However, there might be other considerations depending on the specific transmission and any modifications made to the engine bay.