So - I swapped out the 244 at U540. Still no dice. Then swapped the 244 next to it at U541 also. Making that change, suddenly everything started working. I guess that putting U540 in the wrong way round, not only blew that one, but also the one next to it too. Moral of the story? Don't be a dummy. Insert your chips the correct way round.
Diagrom is now booting successfully 100% of the time and Memory tests look good. I put in a Kickstart ROM and I was greeted with the following:
I am pretty much feeling over the moon at the moment. Something I certainly need in these dark times that we are living in. I started the build back in October, so it's taken me near enough six months on and off. Totally worth every second though.
I would really like to say thanks once again to everyone who has helped me out along the way. Specifically, Acill, obitus1990, Olem, eugenenine, nadoom BloodyCactus, Zippy Zapp and intric8. You guys rock!
Next Steps for me?
1) Get a KS 1.3 Rom. No need for any other versions.
2) Install into my case and attach Floppy Disks.
3) Get a CRT monitor
4) SCSI Hard card + Drive
I already have an A1200 for WHDLoad. I intend to make this machine as similar as possible to my beloved A1500 which I owned back in the day. That will mean playing games from floppy or from Hard drive installation ( if supported ).
If you are considering attempting such a project yourself - I would totally recommend it. It was certainly something of a stretch for my hardware skills and it was touch and go for a long time whether it would be successful or not. I have learnt so much along the way, it's really amazing. Perseverence and help from clever people are the key. I totally have the bug for building Amigas now, so I expect there will be more builds in the future.