9" drum to disc conversion confusion

You CAN use the F-body (Aspen) spindles, although they are not the ideal solution. They are taller than the A-body spindles, so angles between the upper and lower control arms won't be the same. Depending on who you ask, this is either a non issue (Steve Dulcich) or really bad (Rick Ehrenberg). In any event you'll need 73-up upper control arms with the larger ball joint, or tubular equivalents.