Carl,
The cap you found will work in the 40 and 60 watt Sunn tube amps (Sonaro, 200S, etc.), but not in the Model T. I checked the schematic on this website and found that the original cap is a 2-section cap....one section is 60uf and the other 80uf.
The cap only needs to be rated at 450 volt according to the schematic (higher voltage rating is OK). As I recall, you can use higher capacitance in a power supply without any harm (see Gerald Weber's books). So you could use a 2-section cap of 100uf / 100uf. Or try the 80-40-30-20 at 525 volt cap (Antique Electronic Supply). The 80uf section is a direct replacement. Wire the 40uf and 20uf sections in parallel and you are in business. Which ever way you go, be sure to check the cap diameter for fit in the amp and buy a new mounting clamp. Also...unless you know how to work on tube amps, take it to a tech. The voltages are lethal (seriously).
Good luck!
Ryan