TD5 Timing Chain Tensioner

Hi all, please be gentle this is my first post and I promise I have googled and searched threads...

I have recently purchased a W Reg Defender 110. The body is in pretty good condition but the mechanical bits have been neglected and it came with a cracked head. I have built everything up with a reconditioned head but I can not for the life of me fit the chain tensioner - it just bottoms out about 5mm short. My reconditioned head is a 2001 (still 10p) rather than 1999 that I dismantled. My question is - does anyone know when Land Rover switched from a black top to a blue top tensioners as this is the only thing that I can think is causing the issue. Just loathe to shell out £100+ to check my theory.

Many thanks.

So, I found the answer by borrowing a newer chain tensioner. The bottom one was fitted to my original head the top one has more material machined away from above the thread and goes in just fine. This is the newer part the other is the now superseded part. Just need to stop it peeing oil out and I'm sorted.