This could be a problem facing almost all owners of older vehicles.
If you stick to hard headed finances, you should probably have given up two or three grand ago, instead of thinking whether to invest even more of your "hard earned" on a new galv chassis and a replacement head, you've already rebuilt the ACE, and that wasn't cheap I'm sure.
You know you'll never get your money back if you do, but there's more to it than that.
You've invested so much time and effort in bringing the vehicle to what you want it to be, you've put your personality and some of your life into it. It's no longer just a metal box to get you from "A to B", it's become a friend, albeit a sometimes bloody-minded and cantankerous friend.
When you drive down the road, people say "There goes Martin", they don't say "There goes that idiot in that heap o' crap Land Rover", well, maybe they do!
In the end, it's up to you.