The transmitter modules have a number of pre-configured profiles, and these define what each Channel does.
So in a Tx22 or Tx24, Channel 2 is configured to convey the Selecta (Loco Selection) information, which is used along with the individual GUID of the module so that only receivers bound to this GUID/Selecta combination will respond.
In a Tx20, Channel 2 is used to transmit the 'state' of the Channel 2 input pin on the transmitter module.
So, the first thing you need to know is the Profile of the transmitter module, and to make things slightly more complicated, whether you are dealing with a Deltang Tx2 core transmitter module, or the new Micron MT01a module.
From this information, you will know which channels are assigned to which functions and controls on your transmitter.
Then we come to the receiver:
The MR603 receivers are quite versatile, and 'we' the suppliers using them can have our own configurations loaded into these 'at manufacture' (before supply) to 'us'.
So a Micron-supplied MR603 receiver (more universal, for road-models) would have different capabilities to a RC Trains supplied MR603 (my receivers are tailored towards rail-vehicle control).
This gets a little more complicated, because 'any' output can be programmed to do (almost) anything!
Example:
Channel1 is defined as the 'throttle' and responds to the Speed control knob of your transmitter.
This is defined within the configuration of the receiver, and by default H1 is the onboard PWM speed controller. This can be further configured, as centre-off, or low-off. - If the latter, then 'another channel' (default Channel3) is used to define the 'direction' (polarity of the PWM output).
So, back to your 'two servo' problem:
If you want to use a servo with a Micron-configured MR603, you will have to program 'something' because there are no pre-configured servo outputs in the four configurations loaded into the receiver at supply.
If you want to use a servo with a RC Trains configured MR603, then in Configs 1-3 Pin6 is defined as a servo output following the H1 speed controller output. - So the speed-control knob of your Tx24.
(I have this, as there are Soundcards configured to sit between the receiver speed output and a separate ESC input).
So, if (say) you are using the onboard PWM speed controller on the MR603 as centre-off, you 'only' need the Speed control on the Tx24 to operate this.
This means you could use the Direction control knob on your Tx24 to drive a servo.
To do this, you need to know that this information is carried on Channel3 from your transmitter, so to use Pin3 on your MR603 for this, you would program Pin3 to be a servo output controlled by Channel3.
The other control you have on your Tx24, is the Inertia control. - By default, this affects the rate of change over time, of the speed output of a receiver.
This can be changed to control Channel4. - This function is designed-in to the equipment already.
So you could (say) program Pin4 to be a servo output controlled by Channel4.
I can help you with the programming of this, but next week, when I am back home with the paperwork in front of me.
Alternatively, you could purchase a 'bespoke' MR603, from either Andy or myself, pre-configured to do what you want.
Using a bog-standard Spektrum receiver, could be a problem, as Selecta (Loco Selection) is proprietary to Deltang/Micron. - This will not matter if the receiver is switched off when you do not want to control it, but it would tend to respond for all Selecta positions on your Tx24.
You did ask!

You will probably need to read this a couple of times, then lie down in a darkened room, before asking anything else?

PhilP