Hy Chip1951, the bellhousing bolt pattern was standardized in 1963, Chev V8s and 6s since then have shared the same bellhousing bolt pattern. The previous 6 cylinder bellhousing bolt pattern began in 1937 and went through 1962, Chev engines 216, 235, and 261, and GMCs 228, 236, 248, 256, 270, and 302 both shared this pattern.