1993 Plymouth Voyager Thermostat replaced/ bleeding Rad

Engine Cooling problem
1993 Plymouth Voyager 6 cyl Automatic 435000 miles

I live on the west coast of BC Canada and freezing temperatures are not an issue here.

1 month ago I noticed that the heater was not working and after stopping and letting the van cool, I checked the rad and found it to be seriously low on fluid. I topped it up (3 litres) of 50/50 coolant and water.

5 days ago while driving at 60 mph down a highway I noticed that once again no heat. The temp gauge did not read any hotter than normal, so after 20 miles I pull into a gas station and check the rad. Once again it is low so now I know I have a leak. After putting in about 3-4 litres of water, I bring the van up to temp and wait. After van gets up to temp I can see water/steam/coolant foaming out of the motor. (see picture) It is on the right side of the block (when looking at it) away from the serpentine belt and therefore no a water pump(?).I quickly head home and the temp never gets above its normal reading.

4 days ago, I drain the rad (with help from you guys), flush it with a Barrs Block cleaning product, and flush thru 2 containers of Barrs Block Stop leak product, flushing with clear water in between all treatments. I am noticing that I do not appear to be putting in 8-10 quarts of water whenever I am filling up the rad? The leak disappears after the first container of Block leak and appears to have been fixed. I flush the rad with clear water overnight, and allow it to drain. Yesterday I fill up the rad making sure that I am tracking exactly the amount of coolant and water I am putting into the rad. I make sure the heater is on full to open any heater valves there may be. make sure the van is on a slight uphill incline (although the hrater hoses are still higher than the rad cap). I leave the rad cap off to allow air to escape and run the van until water starts to come out of the rad. During all the flushing the heater hoses were clamped off. (see pics)

Here's the problem: When I turn on the heater I get a very short blast of warm (not hot) then cold air. I could only get 6-7 quarts of coolant/water into the rad. (by the way I did replace the thermostat in between the flushing). I have to believe that there is air trapped in the heater??? If so is there a bleed valve/ that I can not find? Am I barking up the wrong tree? Just to add, when the van is up to temp the left hand heater hose is hot while the right hand hose is warm (like the amount of warmth you would get from being close to a hot motor but not having hot water run through it. Many Thanks for your help!!!