If the Y block is "free" I guess that's why you want to use it. Make sure you put the overhead oiler kit on or plan on charcoal under the valve covers.
The 289/302 is a much better option.
With an electric fan it will fit but clearance over the front crossmember is the issue. Mustang II front end works better. Box the frame and install motor mounts farther forward.
This discussion belongs on the HAMB. Try searching the archives there:
http://www.jalopyjournal.com/forum/index.php