That is what you have, but that ain;t right.. The 11mm diesels all had allen heads.. I pulled a few apart with repeat HG failures and found 11mm triple square bolts. THe issue was they used gasser bolts..
Someone put the wrong thing in there at some point.. You're top bolt is kinda interesting though.. Alot beefier than the one out of your diesel...
At this point you need to inspect around the bolt holes in your block very closely for cracks.. Generally these things don;t crack from running but from torquing the thing during reassembly..
I'm gonna plead and beg, sell a kidney and get the head studs.. Here's a fun little story about why-
My current 81 daily driver.. The PO replaced the HG and it blew in about 5000 miles.. I bought it ($50 Yeah!) I yanked the head and sent it to be refurbed.. WHen I got it back I cleaned the block looked for cracks, chased all the hole with a tap and blew them out. Last step of the torque procedure on the last bolt there was an eerie sound and the bolt got real loose..
Round two.. Grabbed another engine from my pile o parts.. Had this block magnafluxed. It was good to go.. Another gasket and another set of bolts to be safe.. Put it together and worked great.. Put 1000 miles on it and did the retorque.. Oil in the coolant almost right away.. Pulled the head, block was cracked at the bolt hole where the oil goes up to the head.. I did manage to baby another 20K out of it by installing head studs with thread sealer but it's back to spewing oil to the coolant..
I'm in the process of building another engine right now.. 12mm this time

At this point I have far more than the cost of head studs in a boat anchor..
Interestingly enough the original HG tossed it's cookies in my former Frankenbunny right after the above ordeal.. I used head studs right from the getgo.. The new owner has about 40K on the thing now..