Picture of my old bolt.

 

Helicoil time , use 5¨x3/8 USS stainless as replacements.

 

WTF , that lower bolt looks like it could be 5/16 , I hope for you sake it is , that would be an easy fix , good luck.

 

Just for reference.

Moparts Tech Archive
Small Block
Small Block bolt sizes

oil pan
5/16"{18}x 3/4" amount needed 18
valve covers
1/4"{20}x3/4" amount needed 10

fuel pump
3/8"{16}x1 1/2" amount needed 2

thermostat housing
3/8"{16}x1" amount needed 2

intake manilofld
3/8"{16}x1 1/2" amount needed 12

water pump & timming cover as a combo-set
3/8"{16}x5" amount needed 4
3/8"{16}x3 3/4" amount needed 3
3/8"{16}x1" amount needed 3
3/8"{16}x2" amount needed 1

distibuter hold down
5/16{18}x 3/4" amount needed 1

Don't forget the washers to go with the bolts.

 

Is that cast iron WP or aluminum WP?

 

Aluminum

 

One of the 4 long bolts is longer than others. I once stripped the treads because not noticing that.


edit: not sure anymore looks like there is 2 long and 2 shorter. 1960-1976 All Makes All Models Parts | MM8276 | 1970-74 Mopar A / B / E-Body 318 / 340 / 360 Small Block V8 9 Piece Water Pump Mounting Bolt Set | Classic Industries

 

I think @TrailBeast posted this.

 

Note that your water pump and the one pictured in post #36. are different. Post #36 is a pre '70 cast iron pump, yours is a post '70 and up aluminum pump. The inlets from the radiator are on opposite sides.

 

EACH of those bolts is location specific.
If you stick a too long bolt into the DRIVER'S side,
it is possible to drive it right into the cylinder and crack it,
And then you are in big trouble.

The coat-hanger in the hole will tell you where the cylinder is, and so, DO NOT install a bolt that long!

I respectfully suggest you take that timing cover off, and clean those tunnels out, and chase the threads in the block. Then you will likely notice that the gasket is shot, or perhaps the cover is rotted.In either case coolant could get into the oilpan, yours wouldn't be the first one to have this happen. And you might also find that the timing chain is ready for replacement.

With the cover off, and laying on a flat surface,
you can mock it up and determine exactly which bolt goes where.

Some guys are afraid to take the timing cover off, because it is tricky to reinstall. but IMO, your first time having sex was way trickier. Well, OK, my first time was,lol.

 

Dusterguy thanks for posting the ad from parts mix.
The list from Moparts just did not seem right.

 

The red paint had me fouled up. I thought I was looking at a early 273 or 318 like mine with cast iron water pump.