Swap k-frame without dropping engine?

did that very thing to my car when i rebuilt front end and changed brakes and re-enforced my k-member.
really easy, i supported my motor from below; simple strong blocks with a small footprint... you need to have enough room for your floor jack.
unbolt your motormounts, use floorjack with 2x6 wood block placed towards front of pan to lift motor slightly, prop the motor under the rear of oil pan with blocks that don't take up much space (i used a piece of 6x6 on end with thinner pieces of wood on top of that to get the right height), lower the motor onto the blocks but not so low that the the motor mounts are making contact, pull the jack out and use it to drop your k-frame. if the blocks you use are stable you can leave it in place indefinitely and get your work done.
I used all wooden blocks- no damage!
good luck! -pauly