The big issue was ending up with a transfer that will survive multiple future inkings and wipings. I don't think Speedball would do that, but my serious inks take too long to dry. Using an ink pad was much faster, the drying time will be shorter, and clean up was nothing. Even on a week night, the process was relatively painless.
I ran a 6" rubber brayer across a pigment dye ink pad several times, inked the block, and when it looked like there was enough ink on it, I laid a piece of acetate carefully in place on top of it. I burnished it with a spoon and then laid the acetate, inked side down, on my second block. This is my inked key block and the acetate (ink side up):
And this is the new block with the printed image down. Some parts of the image didn't transfer as well as others, but still well enough to see what's where.
Once the whole thing dries I'll touch it up with a fine-line sharpie just to make sure the image lasts through the future multiple printings.