Welcome, Andrew! Wow, you've arrived with your tail at a perfect time. There's a bit of an RV-3 renaissance going on right now. Three new ones have just flown in the last few weeks, and several more are underway by experienced builders here.
I'm the wrong person to answer (I'm sure someone better will be along any minute now), but I've been studying the -4 plans for a long while and the -3 plans for couple of weeks. I think the right answer's gonna be "No." But if the tail's in good shape and you're set on a -4, I bet you'll find a buyer for the tail without too much trouble.
Best wishes on your investigation and on whatever you end up choosing to build.
It's a great group here. Tell us more about yourself!
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Stephen