By the time I got finished writing this up (including a couple interruptions from wifey) you guys had carried on a good deal of dialogue, but I am leaving it as it stands. Thanks
I would think it would be more expedient to plumb a sort of "by-pass" arrangement into the hose rising up to the radiator so that naturally hot water could rise up through the regulator/vaporizer.
This is going to require that the hose in place now be cut at 2 places so a short section of pipe can be inserted into each radiator hose.
One pipe in the ascending hose near the engine head and the second pipe in the descending radiator hose somewhere near where the hose attaches to the block.
The coolant ports on the J-model regulator are 3/8" NPT and as such your 2 sections of pipe to "tap into" the radiator hoses would need to have either threaded fittings welded into them, or have 3/8" heater hose nipples welded into them, to transport the hot coolant to and from the regulator/vaporizer.
The regulator needs to be mounted above the point at which you are feeding coolant into it.
Because the net effect of the regulator absorbing heat from the coolant and transferring the heat to the liquid propane. the coolant temperature will be lowered in this process and will induce its own convection cycle circulation loop. Hot water in from top hose and cooled water falls back to the lower region of the engine block.
Ideally you would also add a VFF 30 vacuum operated fuel lock off valve between the LP tank and the J-model regulator to insure that no propane flows in the system if you forget to turn off the tank hand valve.
Legitimate LP engine fuel systems are required to have an automatic fuel lock off feature that senses engine vacuum or oil pressure so that the system automatically shuts of fuel if the engine quits running with the key still on. You can't just have an electric fuel lock off valve that is energized when the key is on, there must be an interlocking switch that senses engine vacuum or oil pressure before activating the lock off.
A direct vacuum operated fuel lock off such as VFF 30 does the job nicely without any electricity involved.

Yes, there is a hose fitting bolted to the head. There is also some kind of repair "goo" all around that area so I'm not real excited about removing it. It would be great to find some type of in-line fitting to put in the radiator hoses. I was also worried about lack of flow. I wasn't sure if the regulator was going bad or not but I thought the freezing and thawing surely had to effect the diaframs inside it. I think I can buy a new one with water ports cheaper than rebuilding this one.

I've seen them, old Carloader with no water pump.
The one of them I worked on had a J&S propane regulator mounted in a special radiator hose outlet that bolts on the head or it fit in the hose itself. That would require a different carburetor,though. Is there 2 bolts that hold what looks like a thermostat housing on the head where the hose hooks on? That might be the only way to go unless you can drill and tap for fittings in that hose housing and maybe find a drain plug in the block to use as a fitting hole. But the water flow may not be good enough. Your regulator probably needs a rebuild and that is causing it to frost up real quick due to running so rich.
I don't think the broken cap is causing any problem.

No pump, the hot water rises and the cool water falls. Top hose comes out of the center/top of the head and goes to the top of the radiator. The bottom hose comes off the bottom of the radiator and goes into the side of the engine block. The tabs on my cap are broke off so I'm sure the system is building little or no pressure. I'm fairly mechanical. Have replaced the tires and entire electrical system on this thing, icluding switching the old mechanical distrubutor for an electrical one. I assume I would need to pull hot water off the top of the radiator and the cooler water off the botom and pipe it to the regulator. Im not sure about the best way to make these connections though. Can I get some type of in-line fitting to place in the hose or will I need to get fittings braised into my radiator?

NO WATER PUMP? Surely you jest. I believe the presence of a RADIATOR with HOSES connected to it shouts "water pump somewhere in here".
At what level of expertise would you rate yourself when it come to actual mechanic work?
Not being sarcastic here, just wanting to know if you are just an owner of an old machine or if you actually have some working knowledge of what you are thinking about doing.

Thank you, it never has ran very well but it was cheap. There are no provisions for plumbing in a regulator. The cap on my radiator is also bad, so I assume I should find a replacement for this also. How do I go about hooking up a new regulator to the cooling system. There is no water pump in the system. Thank you.

If you have a regulator without any provision for absorbing heat, that regulator is probably not intended to be used with input of liquid propane to start with. Regulators that lack vaporizer capability are intended to be used with very low fuel consumption applications (usually less than 8 horsepower) and are plumbed from a tank configured to deliver propane vapor only.
I am getting a visual on this and I think your term "rich condition" is surely an understatement.
A J-model Impco regulator/vaporizer plumbed into the engine coolant (properly plumbed, of course) should give you dependable performance.