I did a simple upgrade to a ronstan auto ratchet block with no base adapter needed and was able to maintain the the original swivel cleat. I haven't seen it done this way before, hope it's useful to someone.
Only two parts are needed. A Ronstan RF56510 block and one bolt with nylock nut.
I drilled out the horizontal pin above the spring of the original block. Then bolted the new block in its place. Done!
The ratchet block also has a becket so if more power is needed the original fiddle block can be put in place of the block on the boom in the same manner making the 3:1 a 4:1?
Full disclosure, I haven't sailed with this setup yet and won't be able to until spring.
Enjoy!