Where are the freeze plugs on 1998 chevy venture Cylinder Heads

on both sides of engine,on front and rear of cylinder heads and the dreaded on back of engine between motor and transmission

Do you mean the valves in the cylinder heads or some other valve?

There are 3 plugs about 2 inches in diameter on each side of the block.
There are freeze plugs in the back of the block where the transmission connects, and smaller plugs in the cylinder heads.

yes.

There are plugs on both the driver's and passenger's side of the engine block and both cylinder heads [outboard side of each head]. There are also several plugs located in the rear of the block. The transmission must be removed to access these rear plugs. You should have changed your antifreeze more often!
Charlie

It depends on which freeze plugs you are replacing. The ones on the left side of the engine block, the ones on the right side of the engine block, the ones on the front of the engineblock, the ones on the back of the engine block, the ones on the front of the cylinder heads, the ones on the rear of the cylinder heads???

Look the cylinder heads over very closely. GM had an issue with certain heads and the extended service anti-freeze they used. These heads would crack.
You want to look for discoloration in and around combustion chamber.
They also had an issue with gaskets and the anti-freeze.
Good luck

Look on the block below the cylinder heads for a leaky freeze plug if that's the problem you are having.

as on any engine the freeze plugs are located along the sides of the lower engine block They look like large 1/2" to 1" brass or silver concave disks pressed into the engine block. They protect the block from cracking by poping out when the block coolant freezes.

go to autozone.com you can get all the spec with the online manuals on there site