I'm a bit of a gun nut, so I'll see if I can help.
For starters, do you have a cirminal record? You said you were not fingerprinted or photographed. The lack of fingerprints being submitted to the State would leave me to believe this probably isn't entered in your history.
Regardless, the section relating to his issue deals with "firearms", which is specifically defined as "Any pistol or revolver with a barrel length less than 15 inches, any shotgun with a barrel length less than 18 inches or any rifle with a barrel length less than 16 inches, or any pistol, revolver, rifle or shotgun with an overall length of less than 26 inches."
A shotgun exceeding the above measurements is not termed as a "firearm", and is therefore not subject to the provisions of The Uniform Firearms Act, Section 6105.
Even more interesting, is that the section prohibits any person from possessing, owning, etc a firearm if that person was convicted of a violation of the "act of April 14, 1972 (P.L.233, No.64), known as The Controlled Substance, Drug, Device and Cosmetic Act" (which is the act under which drug offenses are prosecuted). As you can see, this law was enacted in 1972, 2 years after your conviction. You obviously weren't convicted uner this Act, and the section makes no provisions for pervious statutes or simialr statutes under Pennsylvania law.
So the short answer is - I think you are fine to buy a long gun and even a pistol, if you so choose.
One of the easiest ways to find out is to simply go buy the gun. If you are buying a firearm (as defined by law), or you buy a shotgun/rifle from a shop who chooses to use the Insta-check system even though it's not required (like Wal-Mart), you will certainly find out that you cannot make the purchase when they deny you. There is no specific law prohibiting you from attempting to purchase, and you would not get in any trouble if you are prohibited.
Just to reiterate, it doesn't apply to shotguns or rifles, and a local gun shop should know that.