Possible Oil Pressure Leak Due to Missing Rear Oil Galley Plug

While reading "John Lingenfelter On Modifying Small-Block Chevy Engines", My Son found an interesting pic and caption on page 145, lower right pic.
The caption states "don't forget this little 1/2" oil galley plug found under the rear main cap. If left out, it will create an internal oil leak that can reduce oil pressure by 20 psi."
The text states that most shops remove this plug under the rear thrust main cap to thoroughly clean the block. With the plug missing, results are low oil pressure often misdiagnosed as amongst other reasons, a weak pump or excessive clearances.
My Son checked and found this plug missing on our freshened block. The exact location of this plug is not apparent as the tin "plug" is being held with two fingers over one of the inner block holes closest to the thrust bearing notched side.
He checked the new oil pump and gasket set, no sign of any tin plug.
Questions:
Does someone have a pic of where this plug exactly is installed?
Can we install this plug in our garage?
Or does it have to go back to the Machine Shop to get installed?
Are there other plugs, besides freeze and oil galley plugs we should be looking for?  
Jogasz28
1968 RS Camaro
1969 Camaro in Resto
1971 Monte Carlo
1995 Monte Carlo

If this helps, I searched and found a link to another Forum where I think this plug was discussed:
http://www.hotrodders.com/forum/1-2-oil-galley-plug-under-rear-main-cap-sbc-117829.html  
Jogasz28
1968 RS Camaro
1969 Camaro in Resto
1971 Monte Carlo
1995 Monte Carlo

Yes theres one under the rear maincap.1/2" freeze plug I think. You can install it at home if you have something to drive it in with. I would tell the machineshop and they should give you one and install it as well.  

After reading the post in the other Forum, I realized they must be referring to
a "cylinder" style plug driven in to a depth below the opening. I had my Son check to see if he could see from the oil sending port down thru the rear oil galley opening. He could not, and he did find a plug set below the block main bearing surface.
What concerns me is in the pic I referred to in my OP, it shows a thin plug, not something that would be driven to depth.
Would this be set just below the surface to seal the opening to prevent leakage between the block and rear main bearing cap?  
Jogasz28
1968 RS Camaro
1969 Camaro in Resto
1971 Monte Carlo
1995 Monte Carlo

the steel and probably the dorman brass freeze plug kits have the oil galley plugs included.. both the threaded and the push in...

Dorman / Freeze Plug Kit
For your 77 Chevrolet  5.7L
Part Number: 557-001 for steel plugs
Part Number: 567-001 for brass freeze plugs.. the oil plugs will still be steel..
under 10 bucks behind the counter at almost every parts store...

here is a picture of the contents of the brass kit..

https://www.dormanproducts.com/images/items/hwrap1/expansionplug-007.jpg

the question of how deep it needs to be driven... is still being researched by several people and me ....

looks like that plug has to be down the hole a ***

check this small block chevy oiling diagram...

http://garage.fasterdeals.com/SBCOiling.gif

if that plug is not driven below the horizontal passage into the oil filter. the oil will flow unfiltered directly up to the oil galleys..   totally unfiltered oil...  hmm...    

so the plug stops the oil from flowing up that passage.. turns it out to go through the filter...  then back into the passage just above the filter and back into that same passage... where it will continue to the oil galleys..

thanks for bringing that up....


just curious how many of you use your carbide cutter porting tools and open the passages in the rear main cap...    opening the oil pump and doing the same inside it...  

http://www.carcraft.com/techarticles/116_0109_542hp_big_block_chevy/photo_10.html  

this is minimal to what i do and have seen done...  i also do it ... in a vice.. away from the block...      you can even do it after the engine is together... but before the oil pan is on.. unbolt it.. remove the rear seal and the main bearing..  cover the engine..  take the rear main cap a long ways from the motor.. and grind away..  then use a tube brush to make sure you get every scrap out of every hole..  sorry about going off thread...

i was thinking about using a long ball ended high speed tool to radius the square corners in the oil galleys on the last small block i built for my self..   i just did not have the time or the really long ball end tool at that moment..