It's difficult to say if your master control unit (the module located in bottom far right) is capable of switching IEC and NAB selection. Judging from the photo, it probably is the 1.810.315-81 unit that has three push buttons (speed, tape a/b, IEC/NAB), headphone jack, channel select and monitor volume. If it is, you should be able to hit Stop pushbutton and hold it down while you push other buttons to change your speed, Tape A/B, or IEC/NAB eq.,etc. This function was added to firmware version 4085 (40th week 1985) and younger.
On the other hand, if you have 2 speed version master control unit (it might be since you mentioned you have 7.5 and 15 ips choices), your master control unit has a jumper JS2 that will allow you to skip having to push in Stop before making your selections to work. The JS2 must be in position B to bypass Stop button...but I like having to hit Stop first to change anything to avoid mistakes.
If the deck's MPU board is younger than 1.820.780 then you can remove jumper JS 5 (second jumper from the center hole in card edge) to send input signal directly to output to calibrate your Line output cards. If you do have the channel select function, you don't have to worry about the JS5 and just select the channel and feed 1.23V to input XLR connector. You should get 1.23V at the output. If not, adjust the 500 ohm pot in the Line Amp card. Do the same for both channels. This is assuming your deck is set for 4dB pro audio operating level.
Without the VU meters, you should have no problem playing back tapes after knowing your Line Amp cards are calibrated but would need a decent AC Millivoltmeter (most Digital Voltmeter works for 1Khz signals) to set your record bias for two tape selections you initally make. After that, you can feed known singal source and make recordings.
As John suggested, the best option for you is to get used VU meter panels and replace your existing channel control modules and one blank plate between two control modules. Mount the VU meters, position JS 1 jumper on the Bus Connector PCB to Internal, connect two ribbon cables to CH1 and CH2, connect two analog connectors to J19 for CH1 and J20 for CH2 on Basis PCB. This is the basic direction on how to convert the console A810 into a portable configuration.
You can check back when you get the VU meter panels. They show up quite often on eBay when the "antique dealers" part out the A810s to bring in few more dollars...sad...
The link John sent you is the company that competes with Filmco. I had no issues buying few parts from Irico but not cheap... You might also want to replace your two speed selection master control unit with a 1.810.317-00 three speed master control unit with monitor volume control to get 3.75 ips speed - if you have the 2 pole capstan motor (most likely - if your top speed is 15 ips currently).
Ki