How to model stability analysis of a linear regulator such as this?
 

In simulation, what is the proper method to model a stability analysis of the following circuit?

Meaning where do I inject the AC signal and where do I look at the loop gain/phase? Do I need to inject the AC signal into vdc and look at vb? If so, what other modifications do I need to make to my testbench to properly model the analysis?

The most straightforward way (not 100% theoretically accurate, but more than sufficient) is to insert your AC source between FB and the NI input, and look at the ratio of VFB/VNI

What inaccuracies arise from this method?

use forum search for Tain Middlebrook LoopGainProbe for some discussions

you can also force the output with a Isource - the impedance curve is related to the feedback factor - severe peaking is a warning sign

load step response gives similar info

The loading of the divider by the amplifier's input is not taken into account

Elvee, do you mind posting a simulation schematic of your test circuit for stability analysis?

I bet MicroCAP does it. If you install it and go to EXAMPLES folder than you find something similar ( stability over time, outside temperature, parts parameters deviations and transition events). Must be here.

Here it is; the circuit had to be adjusted to display something usable as the original values were too crazy, but the principle remains the same whatever the exact circuit.

V3 is the AC source correct? And what purpose does the 1n4148 serve?

Yes
Displaying a nice downwards sloping curve as expected, instead of an ugly flat one (not connected with simulation issues).