I'd machine them on a magnetic chuck 
Would these stay on magnetic chuck on their own?
I got four like that. Put them on vise. It's not necessary to mill the sides and definately you don't want to make them too thin, but I had a vise and wanted to get four done fast.
1) Sides: put a thin plate trough the slot to align them, skimmed the top flat and then put them deeper in vise, skimmed side on top of a parallel. Then trued both sides.
2) Bottom: Both sides are parallel, time to tinker bottom straigh. I removed minimum, checked that "nose" will fine.
3) Top: bottom on top of parallel, clamped on sides in the vise. I just used this setting and milled all of them once.
4) Nose, you want this a little negative, something like -2 degrees, then you have positive grip even when clamp is level
https://www.cromwell.co.uk/images/product/IND/425/IND4251015N_1.jpgIMHO, nose bottom machining is important, top only close to nose where washer and bot goes, and tail, where it contacts block.
Pekka