Escellent advice again chaps. very much apprectiated! Yeah, all readings off my car were at Idle

I've been busy cleaning up the engine surface's ready for new gasets etc, and came across a water jacket like this on the head:





I've got a spare head down in my mates shed (unsure of its condition tho) - Im tempted just to open the water jacket out a bit, just to clear up the corrosion. It's just going to be a bit of a PITA to swap bits over to the other head

It's fine on the block by the way

Any opinion's? Thanks