If this engine ever sees 5500 hundred RPM it won't be with me pushing the pedal and if it does happen than I can assure you the title will have already been transferred :)
just my opinion here but if you never plan to rev the 340 past 5500 and you square deck the block. (estimating here) your highest pop up will be around .022-.053 head gasket=.031 piston to head clearance.
Maybe someone will verify that they have ran that tight of clearance.
Think i would still go with a .058-.060 head gasket.
Would you re measure your head gasket and find the thickest part on it. is it really .053 thick?