Hi all. My question is how can you select the correct head gasket on a td5 engine when you have no old to compare. The problembis i believe a 3 hole thick gasket came off but ig also looks like somone has had it off prior to me owning it. What im trying to say is, someone could have just put the 3hole on to play it safe. Is there anyway i can check dimensiobs to see. Ie piston out of block protrusion etc.

My understanding is td5 head gasket should always be replaced like for like unless the pistons or crank have been out.

Doesn't really answer your question I know

I thought I had seen a procedure where you bring the piston to TDC and measure how far it protrudes above the top face of the block, then using the measurement you can calculate the head gasket you need.
Edit
Try here : http://workshop-manuals.com/landrover/defendertd5/engine/cylinder_head_gasket_selection/