A good tool or seven makes it fun, instead of frustrating. Thanks for being a good sport.
In that particular case, a CO2 cartridge is pure Vance Harlow. Nothing wrong with that. A cheap 7/16" fine thread bolt is even better, as long as you drop by an auto shop and ask them to throw a die on it and de-burr the threads. Two minutes work.
It's that yoke removal tool that gets you into trouble. Going low tech? Grab a BIG wrench like
@boat sju said. One whose jaws reach all the way across the flats. But yes, there's a $40 specialty tool for every function that makes things easier, at a price.
That bicycle castle nut spanner is a great inexpensive alternative to a hook spanner. If the diameter is too large, pad the heel.
But the one critical tool you'll need is a $2.75 double hook pick to remove the HP piston shaft o-ring without scoring the land. The standard shop tech technique of spearing it and prying it out is an invitation to a perfect repair, except that the ambient chamber holes now bubble lightly, because that HP o-ring land is now scratched. Scubatools or Piranha.
Two dowels, one 1/4", one thin, to put the o-ring back in.
Carve a piston bullet from a 1/4" dowel with your pen knife.
Angelo's right angle pin pliers, or a small pin face spanner from Scubatools.com.
An air gun or this trick
Post
MK10 Rebuilding Mods and Best Practices
to get out the HP seat.
A plastic dental toothpick to lift out orings.
You'll need to get creative to remove and replace that turret bolt. A friend who will grind the chamfer off an 11/16" deep socket, and grind the outside wall until it slips into the gap between the cap and the bolt head.
But remember, that turret bolt is only 35 in-lb of torque on reattachment, if it's brass. Easy to break, impossible to replace now that VDH has closed after Bruce's death.
You're all set without breaking the bank.