some of the info I have seen here is dubvious, one thing I have read I know to be wrong, and another thing I saw is downright dangerous.

Calipers
you should never use a caliper intended for a vented disc on a solid disc. EVER. The thinner solid disc COULD allow the pads to literally FALL OUT when they wear down, but definitely WILL reach a point where they fail to clamp the disc, before the pad is worn out.
If you really can't stop yourself from doing this, you should at the very least manufacture 4 equal sized spacers to the shape of the pad's backing plate, and fit them in the caliper behind each pad to allow for the thinner disc.

Remember it is not only your life in your hands when you mess with your brake system. If you are not 100% sure about what you are doing, don't do it.

Spring sizes
240Z definitely have the smaller spring seat. beleive me. same size as the 260Z, 1200, stanza, etc