Hi Stu,
I have built a couple of GS-35B HF amps and always opted for the full wave bridge method. That tube will safely run at around the 4000v area, so 3000 to 3500 should be a good head room voltage. I used the "Block" type rectifiers from K2AW, but obviously that is just one style you could use. It sounds as though you have already got a HV.PS layout some what arranged, but I used the PIV rating of 1.41 above the desired plate voltage for my rectifier selection. Also, with the GS-35B, being that it is an "indirectly heated cathode" tube design, you can use a regulated DC power supply for the filament. The one I use is the Power One
12.6vdc@3.4amp with an adjustable voltage and surge/current limiting. Sounds as though you have a good project going.
Jerry
W8zap