it's $300 bucks worth of carb. it wont get better mileage. better performance after install & fine tuning. and better for 4x4ing by a mile.
[EDIT, i gotta say, 15 mpg with a webber? that's really good! some one has done that right.
otherwise i would have said go with the oem carb for mileage. but that's great.]
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there are tons of info on this if you google it. "weber conversion 20R motor"
from just
http://www.toyotanation.com/
http://www.google.com/search?hl=en&r...sion+20R+motor
to answer your Q,
http://www.toyotanation.com/forum/sh...d.php?t=291718
you'll see that lcengineering has options too.