It sure sounds like it. You can check the date codes and compare them to your build date. The 68 GT500 KR got the 428CJ engine. Std 68 GT500's got the PI engine. 67 GT500's got the PI too but with C7AE-A heads not the C8's. Starting in 68 Ford did VIN code some blocks and heads. Look on the back driver side of the block. Where the head meets the deck you'll see a rectangle shaped area on the block. That's where the VIN would be. It can also be on the back of one of the heads. As FE heads are interchangeable check both heads. Far as date codes on the heads it's between the center 2 valve springs on each head. Date code on the block is below the oil filter adapter mounting pad. Date code follows a year/month/date format. Typical 68 date code would be 8J20 which is 68/Sept/20th. There is also an assembled date on the left ear of the block. That date is stamped and is normally within a week or so of the casting dates. So check the date codes and ask your Dad's bud what his build date is. 428's are somewhat sought after yes. Value really depends on overall condition. Being somewhat correct for the Shelby does increase value. But with the economy some parts are down in value. If it's complete carb to pan and a correct date core engine ask around $2-3k and go from there.