Replacing a gas tank for a non-breather

Hi all,
Well close inspection of the removed leaking tank shows that it had been
shoddily repaired at least a 1/2 dozen times.  I want to replace it, but
replacement emission legal tanks don9t seem to be available for a 74.  If I
replace with a non-vented variety what do I need to worry about regarding
engine breathing etc.
TIA
Mike Gagne
74 midge

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