I don't know where You're getting these engine weights, but engines & blocks are two different things, and the weights You've listed don't add up even a little. An assembled Slanty is like 390#, an LA is only 450-475#, and in case You don't know the iron heads & intake on the LA are a good 30#+ heavier than B/RB ones. Replace the heads & intake with Al-U-minimum & an LA is close to stk. Slanty weight.