Use a table ban saw to hack off the 340 piston crown .

kind of action necessary if you have an obsolete engine with no or little support...
or the nearest spares are 13,000 miles away.

but a lathe or milling machine is what you need.....not any kind of saw

i run magnum pistons in a Australian hemi 6 maninly becasue i couldn't stomach the cost of custom pistons for what was a pretty standard build (carbs, headers, cam and CR changed) $200 for 8 magnum speed pros from the mexican equivelent of summit :) (i.e 2 for experiments) or $200+ per piston as a custom job from Jaycee.. nice pistons but champaign taste didn't fit my beer budget

Put head on reach down bore and scribe the bore shape into the head
put piston on rod and rod and crank in motor see how far piston sticks up out of the bore
scribe round it at deck height

30 thou in my case

check head/chamber shape inside your scribe line. does the head need work with a flycutter to accomodate your piston ??
decide on angle to cut piston based on the angle you could cut the head chamber perimeter
45* might be good for a quench ring

all looked too hard to me...maybe next time, so didn't bother and just took the edge off the piston, flat

open chamber head on mine and bore and edge of chamber matched pretty good but the piston would have hit head without surgery

So i cut 30 off the edge of the piston crown in a band of about 1/8 inch all round
i put head on motor with no gasket and torqued it up
then checked clearances with platiguage strands glued to the new edge at 12 and 6 o'clock
i.e more clearance than zero but still bloody close at the very outer edge
all good.. i will be running a gasket with an appropriate bore.
i then checked distance from my new edge of piston down to the top ring
found it no worse than a many others
then used this as a model for the 6 i would eventually use

gave me static cr of 12.5:1 with nail head valves as apposed to dished and a standard monotorque gasket. 30+ thou
carbs x3 cam and gearing chosen to suit

been running it like that for 10 years

some luck involved i'm sure, but when i did the build i was perfectly happy in my ignornace of many things... i would not run so fast and loose, these days and would be a little more careful, piston rock with hypers is small due to tight clerance. but i was working with the crapest core in the world, that had been converted to run chevy pistons with a massive deck cut and an odd overbore on a New house new familiy constrained budget i own 50% of all of these engines in the whole of the UK and apart from my spare the rest are in cars I had to use what i had.

as it turns out the special versions i.e race versions of the motor i had, used a similar set up from the factory...

so i lucked into doing something similar to what the factory did

short answer as said by many above
if you can get the correct pistons get them
if you want to modify pistons a lathe is a better bet
this kinda things is dpendent on chamber shape

can you get it all to work effectivly when saddled with a perfect new set of too tall or indeed the wrong pistons?
...... yes i did, and so did chrysler Australia.

easier to do with open chamber head
would not be possible with a near flat heart shaped chamber
never had a wedge head so don't know about them

don't use a saw

Dave