Here is a link to a couple of pictures:
I would not recommend freehanding the operation.
I have a cylinder head fixture that is doweled for the head. I used this fixture bolted to the table to locate and hold the blocks. Using my DRO, I located the dipstick hole and angle in the stock block. I switched the the setup over to the TA block . Once I had the block located (0,0) I had to choose where to put the boss and hole.
The Stock block has the dipstick hole inline with #3 main bulkhead. The hole cannot go there on a TA block because of the solid bulkheads and crossbolted maincaps. I picked the best location with good clearance for the crank and machined the boss, then drilled the hole.
As with MOST machining operations it took hours to setup and minutes to machine.
The unmodified stock dipstick tube fits in Rick's TA block and bolts up to the header in the stock location.