4CX1000
This tube requires an SK800 socket with chimney. Last time I checked a ceramic chimney was priced at about one hundred bucks. Since I only paid 38 bucks for the socket and the good 4CX1000 was a gift, I find it difficult to pay the going rate for a chimney.
Time to research some sheet silicone rubber. Try to cut it cleverly to make it into a cone. Then use hose clamps to attach it to the tube.
I still think the 4X811 route is the better one to take, but if you already have all the required parts, especially the expensive parts, then a 4CX1000 solution may be the way to go even if the best you can do is provide 2500 volts of plate high tension.
The only things I need are a good high voltage plate capacitor, a plate blocking capacitor, and an antenna loading capacitor.
The advantages are a nearly indestructable amp with a power reserve that will never be used.