"Slant" motors are inline 6 cylinder motors that are inclined at a 30 degree angle from vertical. "SB" is referring to small block "V" motors with 2 heads. If you take from the block, and not the head, the valves stay tucked in the combustion chamber rather than protruding out from the head's deck into the cylinder bore when at lift. That way in case of a timing failure (Broken timing chain, etc.) your motor is safe from bending valves from valve to piston contact. This is called a non interference motor. If you milled the head down to the point that the valves protrude from the deck of the head into the cylinder bore and the timing chain breaks... some valves will be stuck at lift, and as the piston rises it will smack the valve. No good! That's aptly called an interference motor.
Cheers!
Drake
