I'd risk it and torque it to 65

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Agreed; torque it down to 65. I wouldn't have even tried to run the engine without it torqued down. If the bolt or threads in the block won't take 65 foot-pounds, then you've got bigger problems.

I am very curious what went wrong with your broken bolt. Do you still have the pieces? Are the threads damaged at all? Can you take some good pictures of the fracture surfaces?

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Car is running fine, perfect in fact. Have taken it out a couple of times and even put my foot in it giving it a hard time and she is going great. Don`t know why the bolt broke, i am putting it down to my torque wrench. I have spoken to Kinchrome and they aren`t very helpful at all, saying that they think you should get your torque wrench re calibrated every year, what a joke, but i think it was the torque wrench which was at fault. Yes i still have the bolt, but since photo bucket has changed i don`t know how i can post photos on here. Regarding the torque of the bolts, you have to remember it not a new head gasket, they were already fitted and re-torqued after so many miles and the gasket that is on it doesn`t require the bolts to be re-torqued again (which i found out afterwards) and is already to its shape. The bolt i replaced is done up tight and about 40ftlbs. Yes a bit less but they are slants, tuff motors and they keep going for ever. I really don`t see any issue with it. If i had a new gasket on it and even new bolts to work with then by all means id push it to 65 ftlbs. Anyway im not taking it apart again, whats done is done and time will tell how she holds out.

You can recalibrate the click wrenches yourself..........

Just need a scale, a ruler and some misc parts so your lifting some weights

I also like to test click at low torque so I know it's working.

I've had the internal parts misalign when I've backed it off to far for storage.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

It might run forever like that, but it's not a risk I would take. Yes, the slant six is a very overbuilt motor, and your head gasket is already compressed, but none of that matters if you don't have sufficient clamping force to KEEP it compressed at one corner of two cylinders. I suppose 40 ft-lbs is better than nothing...

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

I would torque it to 65-70 ft-lbs with a known good torque wrench and run it.

Lou

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Home of Slant6-powered fun machines since 1988

The reason the bolt broke is it failed, it's 40-50yrs. old Dude, it happens. I work on crap that ain't 10yrs. old with modern metallurgy and it fails. If part of the broken surface is dull or black, it's been
cracked awhile, and it just picked now to give it up. The new bolt don't give two poops about how old the rest are, torque it to spec and go to sleep already,................