I think Scholman has you pointed in the right direction, you'll have to take it apart and put the cone in the cam tunnel and then reassemble.
After looking at a few of the low buck cam bearing tools for ideas, and then making my own, I fixed that situation by making a 3 foot long drive rod for mine, I can install the front bearing and still have 6"+ of rod sticking out of the rear of the block.
From the front of the block install the rear position, #4 position, #3 position bearings,... then turn block around and from the rear install the front bearing and #2 position bearings. The farther the alignment cone is from the drive head the more accurrate the bearing alignment will be, preventing cocked bearings, and the order I gave will minimize the number of times you have to disassemble your tool inside the block.
Don't forget oil hole alignment, for SBC it has to be over the groove, and the preferred clocking is to have the oil hole in single hole bearings at 4o'clock as looking at the block from the front and in the upright position, to put the oil into the bearing before the peak load, which is straight down. Oil hole in bearing aligned with oil hole in block(at 6 o'clock) is not the correct method.