Flow Simulation on Audio Guitar Amp
Ok, if you want to be a little more meticulous.

Assuming this is a classic AB tube amp, it should run around 70% of its plate dissipation in quiescence and about 100% on average when the full signal is applied.

Preamp tubes usually draw constant average current of about 3mA per envelope (assuming 12AX7), and you can roughly estimate total plate+plate load resistors dissipation from there. Consult the anode curves for particular bias modes. I believe this figure should be around .75W per envelope.

The rectifier dissipation can be estimated from the maximum anode current (for safety) and the internal resistance of the rectifier (from the datasheet curves) or from observed voltage drop. I got about 10W which conforms with my experience that rectifier tubes are usually really hot.

Don't forget to add filament power as all of it is converted to heat.

Output transformers do not usually heat up if they are of any quality. Power transformers usually heat up to 80-90F above ambiance. You can estimate power figure if you know the type of the core used - usually it has a specific W/kg at given Tesla rating. You can assume the induction to be 1.5T (common for commercial trannies). Add resistive losses of the windigns as well.

P.S. Whatever results you get - do NOT mount tubes horizontally - stick to upright/upside-down variants only.

P.P.S. On a more general note, I have seen amps that fried their electrolytic caps which were situated way to close to output or rectifier tubes. I have never seen the heat do any other kind of damage.

Cheers.