Hey-Hey!!!,
The PS is easy. Any of the 300-series Hammond: 369GX, 369JX, 369AX will all allow a simpler, all valve rectifier. The 30 Hy choke is the next upgradeable: I got a Heyboer HTS-8039, a 35 Hy and +100 mA inductor. It is bigger than a St-70's output TX and set me back $70 and shipping. The Hammond 30 Hy/40 mA/600 Ohm item is quite within its ratings for our application.The single L-C supply gets 120cps ripple to less than a half volt P-P according to the PSUD sims I ran. The active plate load I suggested is quite capable of providing the required isolation from that sort of thing.
The question I have is: How much extra do you feel like spending, as the improvements will be far more incremental after an innitial upgrade. Also the 261G6 is rated at nearly twice the DC B+ as the TX's I suggested. A custom Heyboer might be a better option( detailed/suggested:http://audioroundtable.com/GroupBuild/messages/138.html ).
keep asking questions please, there's plenty of answers left...
regards,
Douglas