https://www.thermioniclab.com/en/power-transformers/

These transfomers are listed on ebay as an "upgrade" for a Decware EL84.  They do look slightly larger and they are not expensive ($200 or so counting shipping and tax).  Wouldn't be hard to wire up assuming their claims are correct that all the voltages are correct (300V B+, 6.3 and 5v for heaters).  

Has anyone here considered this seriously or made the swap out?

They also offer a lot of different output transformers.  

thanks,
Jerry