The best thing when it was 2ºC outside max temp of mosfets were 38ºC at 130A 
So at winter I can probably amp up some more current
Everything depends on airflow and how fast you can cool it down… If it was water cooling with decent radiator I could guarantee 200a would be flawless 
Regarding heatsink I suggest to sand off the surfaces to remove anything what could increase thermal resistance, and mount focbox on it or there is another way. cut out small rectangular piece of aluminium like a in original case to lift up because 5mm thermalpad will like air cooling…
P.S. Don’t forget this mosfet package can’t run without heatsink as it doesn’t have any thermal mass
