There is a semi recent thread about flushing raw water
I have just flushed my Yanmar 2GM20
and FWIW, here is some details.
I used 8 litres say 2 gallons of cheap
white vingear recirculated though engines for 18 hours. I used a cheap bilge pump
siting in a bucket. 18 hours because that was a convenient time frame!
I removed the annodes first just on principle.
I removed thermostat otherwise it would remain closed and thus not allow vingear though head
and block. I blocked off the bypass hose that allows for the normal raw water
to pass directly into exhaust
injection point when thermostat is cold.
I'm not sure exactly how your engine
is plumped but many (all?) rawwater cooled engines use the thermostat for two functions.
1. Block water
and block when cold and divert water directly to exhaust
2. Allow water to head and block when hot and block the "by-pass" water going directly to exhaust injection point.
Providing you account for this cold bypass function, you should be right.
Initially I planned to use something stronger than vingear say HCl (say 20% for say 30 minutes) but I glad I didn't, even being careful, I managed to spill and spray the vingear around too much