In the Bentley for the gas 1.8 JH engine they have a side by side picture of the rod stretch bolt and non stretch bolt. The stretch has more of an hour glass shape. The diesel manual up to 84 say nothing about stretch bolts but the bolts in my mech TD block had the stretch shape and nuts were not notched. There is no telling what has happened to the motor in the past 25 years. Replace them unless you like to gamble.
From personal experience, some parts suppliers list the JH rod stretch bolt as the replacement for the 1.6 diesel rod bolts. Wont work, diesel bolts are thicker.
I WISH I HAD A SCANNER to scan these pics in my chilton manual.Also a little further into the overhaul section they also show another difference between the stretch and non-stretch type.The reusable bolts will not have a shouldered nut(flanged).Im still wondering about the main bolts ,as mine are not "shouldered".I also have reusable rod bolts in the engine.