Will I have to make any major changes

If you're going to keep the car stay with a V6. There's a laundry list of things that need to be changed and modified to put a V8 in there. Not worth it in my opinion! Have you tried removing the spark plugs and turning the engine over? One of the cylinders may be filled with coolant from a bad intake manifold gasket or blown head gasket. These engines are pretty durable but notorious for intake manifold gasket failure that can cause coolant to leak internally. Hope that helps! Jim

Thank You soo much man. Yes that's is more helpful than you know

You're welcome. Glad to help! Jim