Bryce, You ask a difficult question as you probably are aware of. There were many confederate artillery batteries involved at variuos times. Colonel Thomas Carter had charge of defending the James River line and had Hardaway's and Cutshaw's artillery battalions in this line but spread out. When Hancock landed on the north bank, the battery most mentioned is the 1st Rockbridge (VA) Artillery, commanded by Captain Archibald Graham, of Hardaway's artillery battalion. The problem is this battery was armed with four 20 pounder Parrotts and after a good defense of the line, without infantry support which had fallen back, the battery withdrew minus their four Parrott rifles. The next day, Poague's artillery battalion, with Penick's battery attached, was sent north to help to defend this line. Possibly, Penick's battery might be the battery you ask about. Penick's battery, the Pittsylvania Artillery of VA, commanded by Captain Nathan Penick had two 10 pounder Parrotts and two 3" Rifles, both types of guns that could have achieved the task you mention.
Spources used are The Long Arm of Lee, Volume II, page 856-857. Official Records, Volume 40, part 1, page 800, report #800 and also the report of General William Pendleton, report #294, page 755 but see page 759 for info.

General Hancock withdrew after the stiff defense built up by the confederate defenders but none of the source passages mentions two guns holding off the union troops. There were too many confederate artillery units nearby to identify the battery you seek.

This falls far short of the specific information you seek but may provide a clue. Good luck in your search
Ron