440 Engine Guru's Help

I picked up a GTX while down south visiting ,,, years back, well it ran good going on the trailer. on way back home, stopped to see a car friend, he wanted it, i sold it. he was racer. ran good on I 35, till he got it up to full speed, 90 and more, had a vibration coming from the engine.

he torn it down, the 400 had one six pack rod, rest reg 440 rods!!!!! Ha ya never know what you are buying!????