Useing the smallest CID engien of a engine family is a poor swap choice especially if you want 400-450hp as it will just as much to mod the 366BB to that power level as a 350 SBC.
The stock 366BBC is not even close to that power level and will need extensive changes to achieve that.
In a 4x4 ( that does not need to go fast (MPH) what you really want is raw torque, not horsepower.
If you want raw engine torque from and engine that does not rev high use a very large cubic inch engine.
If you want a lot of torque from a small engine rev it and gear the vehicle accordingly.
Or supercharge it. or both.
Swapping in a BBC has a weight penality that has to be accounted for to get a net benefit.
If you re going to a heavier engiene family you want a large CID version of that engine family.
a 366 Cid BBC is not a great choice. Especialy in stock form.
Find a 472 or a 500 Caddy motor. Raw low rpm torque. Bullet proof.