All the bolt holes are blind, in the block and head, except that 1/2 inch LHD alternator hole down lower.
In this pic, the biggest at the top, is that a scratch though the oil adjacent to the left hand top bolt, or a crack...



But 1st, the new bolt, could it be too long? Add another washer (Clutching at straws)

Can you put a little can of corrision inhibitor or some dye in the coolant to make it easier to see.
Fixing the oil leak wouldn't hurt either, take the tappet cover off, belt the screwholes in the sheetmetal flat, if the cork gasket is still in one piece and not shrunk to short, it will work again. You need some large diameter heavy gauge washers to spread the load of the screws better, cad plated please.

Can you have a look at the weaphole on the old pump? If the seal was leaking, it comes out the hole, so you should have a muddy or green stain coming out. The weaphole saves the bearings, so if they feel bad, something might be wrong with alignment with whatever is attached to the front of the pump, or whatever those big belts drive is too much strain on the bearings. What do the two big belts drive? In a 164 it's just one regular belt driving the pump, alternator and fan blades. The power steering pump gets a belt of it's own in a car, so it's a half wrap around both pulleys & it's a collassal pump same as fitted to the 10 litre truck donkey from that era.

So a pic of what the big belts drive + a pic of what's in front of that pulley please.