JC Whitnet sells a kit to up the output to about 80A.
This is a so so fix as the cooling setup is not improved , so full output long term at high temperature is a dream.
Some alts have a "universal" fan which can be upgraded to a better design that is for the direction your alt spins.
For a long time (perhaps even now) the Ballmar units were simply Les Tech rewounds with "better output " guts, and nice paint..
The only real way to have a higher output is a better alt, usually a 135A truck unit for about $150.
IF the guy at the local parts store is willing you can find better alts , the same size as the 55 , which is built for bigger cars , Caddy or big Olds.
He can get down the Caddy box for the right year (OLD IS BEST) and see which are identical.
Old is best because the older units have external regulators , so switching to a Marine 3 or 4 stage unit will be a snap.
The stock built in auto/truck charge regulator is almost useless for charging house batteries
FF