My magic R-value for replacing the 0.15 ohm heater resistors turned out to be 0.25 ohms , for a combined value of 0.50 ohms. With a 0.25 R swapped for each 0.15 R, I get 2.52V (avg) on one tube and 2.535V (avg) on the other.

[Edit - May 16 2019: Now that the amp has been burned in, I checked the heater voltages again and found that they had crept up a bit (about +0.02V). My new magic numbers are a combined 0.57 - 0.58 ohms per pair of resistors on each socket : 0.30 and 0.27 on one socket and 0.33 and 0.25 on the other. This gets me to a heater voltage averaging 2.5V +/- 0.005]

In case it is useful to someone, here are my DC voltages between pins 1 and 4 of the EML 45Bs for various R-values I substituted for the 0.15 ohm Rs:

0.157 ohm: (0.33 and 0.3 in parallel): 2.7V (avg)

0.18 ohm: 2.67V (avg)

0.20 ohm: 2.62V (avg)

0.22 ohm: 2.59V (avg)

0.25 ohm: 2.53 (avg)

The above data may suggest that the drop in voltage was not linear (e.g., going from 0.18 to 0.20 resulted in a 0.05V drop, while going from 0.20 to 0.22 resulted in only a 0.03V drop. This is because I tested the increasing R-values on alternating tubes - i.e., 0.18 on Tube 1, 0.20 on Tube 2, 0.22 on Tube 1, and so on. The same 0.25 ohm value on both tubes resulted in a 0.015V difference between the filament voltages. Factoring in the 0.015V difference suggests a linear drop of approx. 0.02V per 0.01 ohm increase.

*** Note: the above values were reached after 5+ min and then became stable. I tested the VDC for the 0.25 ohms resistors by waiting 20 min just to be sure. For anyone looking to do the conversion, I would recommend waiting until the amp is well warmed up before settling on a final R-value. In my SII, 10 sec or so after power-on my reading with the 0.25 ohm resistors was only 2.4V

These measurements were taken on a fully upgraded SII after making the following mods: 3K resistors replaced with 8.2K resistors, removal of 0.13 ohm resistors that ran in parallel with the 0.15Rs, and swapping red and black wires from the plate chokes. I did not make any changes to the 130 ohm Rs.