If its longer you may have a 320 ci.
Is the exhaust manifolds 1 piece or 3 piece ?
263 ci was a replacement for the 248
A lot of cutting and welding to get the 3" longer engine in where a 248/263 was.
Have not read where anyone has done this so good luck !
http://www.teambuick.com/forums/show...-a-263-for-320
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