Hi Dee: Where to begin without writing a novel.
1. First do not install Mod 878 in your TS-830s. Installing a TVS on the FG line (-C bus) of your TS-830s will not and I repeat will not protect the front end of your radio. This mod is very flawed and has nothing to do with lighting, ESD or inadvertant RF entering your SO-239 connector. I can cover this in detail off list if you are interested. Basically what really occurred was 6146 arc over which applied nominal 850vdc plate voltage to the tube control grid, to the FG line, to the ALC amp transistor via its base biasing resistors in the -C line , to the ALC bus line and to transistors Q2 and Q7 as the high fault current went to ground thru the bias pot back to the -C supply on the HV board. Nothing to do with lightning or transmit RF at all. Placing a TVS to ground on the -C line offers no protection whatsoever to L41 or Q1 on your RF board. A review of the circuits will confirm that.
2. What you need is what 160 operators who use seperate receive antennas like the Beverage commonly do and that is a Front End Saver. This device is activated via your aux relay contacts of your transmitting 830 and removes the receiving antenna off your other 830 and shorts the SO-239 coax connector. In this way no transmit RF can get to L41 and Q1 in the receiving 830 front end.
3. You can homebrew a passive Front End Saver using TVS diodes, PIN diode attenuators, Resistors or Chokes. The Little Fuse makes TVS diodes for this application. The TVS will protect against ESD. Pin Diode will protect against strong RF fields by clamping the RF to approx 10 dBm. A 27k to 39k resistor or 2.5 mhy choke to ground will keep antenna input grounded for dc and drain off any static charge. This circuit would be a passive protection device.
4. Better would be Front End Savers using fast acting reed relays. These can be purchased commercially or home brewed. Search on KD9SV and OK1RR for circuits. I think the KD9SV model SV-FESSS unit runs built for around $100.00.
5. As for L41 step up transformer and Q1 RF amp they are both commonly damaged due to near by lightning or inadvertant transmitter RF ( the latter is the more common cause due to operator error ). I have rewound 4 to 6 L41 transformers and it is a bit tedious. I have the turns ratio from Ken Kempski and the measured inductance of the primary and secondary windings. Gordon Benjamin N6WK also does a good job or rewinding these. I think he made a video so you may want to contact him to see if he can provide it to you.
Lastly as Carl points out the 40673 is a fine sub for Q1 3SK73.
6. You should have no problem at all using your 2nd TS-830 to receive on if you install a Front End Saver at its SO-239 and actuate it with your aux relay contacts on the transmitting TS-830. It is done all the time by DX-ers and Contesters.