I agree with Mr. Keller. The answers to your questions are easy enough to obtain by attempting a purchase (be sure to answer all questions truthfully) and if successful there go on the the carry permit process with the Sheriff's Office in your county.
You should never fill out any state or federal form (ATF 4473, PSP Application/Record of Sale, Application for a License to Carry Firearms) without knowing whether or not you are prohibited. If you are prohibited and inadvertently answer incorrectly on any of the forms, you can be charge with making false statements. Also, if you are unsure and answer in the affirmative to a prohibiting question, the FFL is to deny the transfer without calling into the PA Instant Check System.
While, generally speaking, ARD dispositions are not convictions, you only state that you got ARD; not that you successfully completed ARD. If you were convicted of any M1 in PA, with the exception for cruelty to animals, you will be prohibited from possessing and purchasing firearms and ammunition, at least under federal law, if not additionally under state law.
You need to speak with an attorney that is well versed in state and federal firearms law and who can review your dockets to ensure that you can legally answer in the negative to the prohibiting questions on a 4473 or other similar form.
www.PrinceLaw.com and www.FirearmsIndustryConsultingGroup.com
The information is for general information purposes only. Nothing stated above should be taken as legal advice for any individual case or situation. No attorney-client relationship is established.