Cheapest way to 400 whp

Actually, it’s more of a fat brother to the LS1. They also came in 5.7L and 6L variations. I believe a 6.2L version is there as well.
These engine still go for about $1500 on kijiji without a tranny.
However, the LS1 is heavy enough as it is being made out of aluminum. No sense trying to add more weight with the iron variant.
The torque will rape anything. If you can put the power to the ground effectively.