The thin-headed bolts and mounting plates described in this Shop Manual have been used/found in all 1954 235s that I have worked on, and on the 1959 and 1960 261s that I recently had apart.
There are no tangs to bend-up on the lock plates, so, in recent years, I have used loctite on the threads of the six thin-headed flywheel attachment bolts. The manual says to use new plates but I have never found these being sold - loctite is good assurance/insurance.
Here is a "thin-headed" bolt. I suppose if you have no lock plates, these bolts and lock washers would work fine (still using loctite - why not?).
blubird's attachment nuts look to be thick/heavy-headed (are they castle nuts)?
