The 230 and the 292 are inline engines... as longbox55 mentions.

http://www.stovebolt.com/techtips/buyers_guide_60_66.htm

GMC: 1960 - 1963 Big Block 305 V-6 only
GMC: 1964 - 1966 Big Block 305 V-6, (351 V-6 -1966 only) - or option of the inline Chevrolet six cylinder engines