Why do you want to remove it? Just curious.
I assume you've got a 510B and not a 510 since a 510 has a vertical pump and no tapered shaft.
I've removed many without taking off the timing cover. You might have to get some other stuff out of the way. Once the injection pump is off - have someone hold something heavy against that gear from the pump-shaft side. Then from the other side - you use a large drift pin and hammer (or whatever you have) and give the end of the tapered shaft a hard whack. If hit hard - with that gear backed off, the shaft will pop right out. No different then removing a flywheel from a tapered shaft on a small engine. You DO want to protect the threads of that shaft end though - unless the shaft is broken and doesn't need to be reused. I've only removed them when broken. I can't think of any other reason to take it out. I know you said you've hit it already - but that won't do any good unless that gear is backed up from behind when you hit the shaft.