LA 360 or 5.2 magnum

Your '91 5.2 is not a magnum. The 1st year for the magnum was '92. So, your looking at a LA 360 vs a 318 with roller cam and 302 heads. All 318's are internally balanced. Both engines would serve well, depends on the use of the car. The roller cam 318 would work well with todays oils, and it already has heads for todays gasoline. The 360 offers more cubes, torque, and in the end more power. If you use the 360, you would need a balanced flex plate from B&M or have the 318 flex plate balanced and use that with the 360. Truck motors need a car oil pan and oil pickup tube to work in a car. 360's and 318 take different oil pans.