.............The easiest thing to do is (assuming you have a machine shop somewhere around your neck of the woods) is take the mould to them and have them flycut the top of the blocks, as below:
Measure the width of the BB and tell them that's what you want removed. The setup is quick and is not any kind of headache at all. You will lose the sprue plate stop pin, but since you have a drill press you can replace that yourself. Unless your machine shop is doing some type of production work, the guy at your machine shop should be happy to do it for a decent price, or buy him lunch.
If there is a High School or Junior College around with a manual arts program they might also do it for free too. Just don't get all involved in explaining it's for a gun In todays' climet someone might get all whacked out. For example about 30 years ago I needed the pivit pin for a MkIV Martini. The guy I talked to was the owners son and he had a real issue in making a part for a (God save us) gun!!!!
His dad walked up and asked what was happening. His son held up the part I was needing and asked his dad if they wanted to be making "Gun Parts". His dad was a smart man. He said, "That's not a gun part, that's a split pin" which in truth that's all it really was!.
.............Buckshot