Technical Cadillac coolant bypass

I'm new to the Cadillac engine and didn't realize that there was a coolant bypass port under the thermostat. I now have the correct type of thermostat but thinking of blocking the bypass. Does anyone know what size of freeze plug I need to block it and yes before everyone tells me I know I have to drill a small hole in the freeze plug so that there is no trapped air.
Thanks for any info that I get

 

It’s there for a reason. It’s for circulation while the engine heats up before the thermostat opens. If you have a cooling problems in traffic install a smaller water pump pulley to speed up the pump. On a different engine I did what your asking with a 1/8” hole and it worked ok but never right. After I fixed the real problem I went back to stock and every thing was better.

 

Hey thanks for the advise. I didn't have a thermostat at all not realizing that it was needed to force the water through the radiator. Even at that it didn't get to the boiling point and that was in 90 degree weather. Being in Texas we get pretty hot so I need it to run as cool as I can, so thanks for the advice

 

Nicely done! Looks like you had plenty of room for the engine between the firewall and the radiator. What radiator are you using ? If you should have problems later, there is a mod that some 500 Cad builders do to enlarge the rear coolant hole from the block to the head (and add an extra small hole) that helps circulation quite a lot.Have to remove the heads to do it though. Hopefully you won't ever need it. Any more pics ?????

Edit: Also there is a difference in Cad thermostats and generic ones. Don't remember what it is, but know there is a difference.

 

Thanks! after I rebuilt the body I bought the duce frame rail and built a jig on my shop floor and started at the radiator and measured every 6" and bent the rail to match the body. The fact that I wasn't using a hood allowed me to allow for the room for the 472 caddy. The trick is allowing enough room but still keeping it tight. Way too much area between the firewall and radiator looks terrible. I just got the car done and actually used the Lonester Roundup for the shakedown run, so now doing a few minor adjustments. Taking the car to Booneville speedweek and should have pics there.

 

I like how you positioned the engine a little higher so that the headers can flow over the frame rails. Probabaly more room for the steering shaft as well. The carbs are right near the top of the firewall rather than sitting way down in the engine bay. I think that looks very good in relation to the rest of the lines.

 

Thank You, Yes that is one of my pet peeves, A hoodless car with the engine setting way down between the frame rails. And yes it does make more room for steering and the headers are Lake Style headers and are meant to go over the rails.