Flywheel Help!

So I have a late 72 340 with a CAST crank and am converting it to a 4spd. From the people I have talked to it is almost impossible to find a factory 340 externally balanced flywheel just because they only made em for about a little over a year and Brewers wants $230 for one and money is tight. Is it possible to take a neutrally balanced flywheel and have it drilled to the factory specs of the externally balanced wheel? One more piece to add is that the motor is in the car so I wouldn't be able to bring the crank with the flywheel. I have seen a picture that cracked back has posted a few times. Is this 1 hole all it is for the externally balanced flywheel in that exact spot?



Thanks :cheers: