Hi, I'd say just leave the ground off part where it is, you'll need to balance the whole assembly when you're done anyway. Have a look at these photos of when I did my 1100 crank. While the way I did it will work fine, I have since been advised to only take material starting after the main journal so as to not remove any counterweight material and to retain strength. Set it up on vee blocks and mark cut lines on crank and scribe a line, roll crank over till line is dead level horizontal then make a little block to put under the big end to rest it on, Mill one web at a time and when you move to the next one just roll the crank over and mill to the same depth and you should take the same off each one.
_________________
1972 Mk3 Mini 1000, 1150cc supercharged.
https://www.ausmini.com/forums/viewtopic.php?f=3&t=95872