Re: 16 foot invader gas capacity
The 1973 models from 16 to 19 ft, inboard and outboard had factory tanks of 12 gallons. This was a standard size for tanks in boats from this era.
Be careful with a built-in tank of this age as it has likely had rust seep in from exterior rusting. We removed ours at least 15 yrs ago and use only removable plastic and metal tanks now. If you shop around, you can find a 12 gallon tank that will slide into the area where the current one is thru the access to the bilge. Also, the vent for that tank may have been clogged by mud dobbers and spiders, so it may not be safe. Most states require a fire extinguisher to be carried if you have tanks when are or can by enclosed.