Upper control arms

Being that your car is a 75 it would have the large upper ball joint regardless of being a drum brake car. That car used a BJ 10162 the larger upper ball joint So you would only need to get the disc brake spindle, brackets and hardware to do the conversion.

For engine the k members are different between the slant six and the v8, but there are vendors that make modified engine mounts to put v8's into a slant 6 k member if you don't want to change it

Thanks
James