As much as I hate to say it, you really aren't going to get much of anything for the work you put into that car.
Any mechanical work is generally regarded is maintenance. In other words, the suspension work you put on your Mustang is regarded as maintenance. It makes no difference in the eyes of the local market, whether you replaced it with stock Foxbody parts or upgraded to the SN95. General maintenance of suspension components, brake components, oil changes, etc is what is expected of the owner to keep the vehicle in running condition. As such it does not add value to a vehicle.
However, major component maintenance (i.e. motor, transmission, rearend, etc.) does add value to the vehicle BUT the insurance company will not pay dollar-for-dollar for what you paid. Generally it is factored into the value of the vehicle itself...depreciation and market conditions adjust the value. The amount you get generally depends on the amount of money spent and when it was installed. Usually you won't get much of an increase for major mechanical work done over one year ago. For example, we all know a Mustang with a new $5k motor would not be worth $5k more than a similar Mustang with the original motor.
Definately keep all the receipts and submit them as necessary. It can't hurt you to go through them with your adjuster to see what impact it will make on your valuation. I would also request a copy of the valuation summary as well. Read through it to make sure everything is correct. Insurance companies generally use a 3rd party value system (i.e. CCC Valuescope)...so when you get the valuation, feel free to call the up yourself. You can discuss the impact of this work with a rep...they are generally more than happy to answer whatever questions you ask of them.
To contradict what was said above...the insurance company does not pay replacement value. It is the duty of the insurance company to indemnify you, meaning put you in the same financial spot you were in prior to the accident. They will pay you the value of YOUR vehicle based on the local market in which you reside. They will not pay the cost to replace it and definately not pay the price that the niche of Mustang fanatics would pay for a comparable Mustang.
Sorry if this post doesn't make sense. Been a shitty day and my brain is absolutely mush. I'll probably need to make revisions to this post later.