Hi Ted. There is already written a lot about the rabbet in relation to the YQ drawings and manual. Basically the space between the parts 17 and 20 is enough to function as a rabbet. About Eisnor I wrote this in one of the threads in the Main Support area:
“But I see the same in "The Practicum" from Gene Bodnar, also building conform Eisnor.
On his page 31 you can see it in his 'step 3' on this picture 022 and 023 and page 32, pictures 025 and 026.
Also page 50, picture 058. But Bodnar has not planked his model till the keel and over the deadwood.”
I don’t know if you have already downloaded that practicum. In a quick search I found —>
this site <—.
And in my build-log there was the discussion in the posts #47 till #60. But beware of my build: it’s a combination from YQ / MS-Lankford / Eisnor / Jenson.
To make it not complicated: leave the rabbet between the parts 17 and 20, or sand the bottom of part 17 a little bit.
The principle of the rabbet is based on this:

The lowest plank, the Garboard Strake, must fit nicely. It depends also on the thickness of that plank.
Hopefully this will help you to make your choice.
Regards, Peter