2.1/4 head Casting number

Hi all, I need help with I D ing my 2 1/4 diesel cylinder head.
The casting number is HRC1353 and a stamp on the rocker cover mating surface ETC4302. I think it is a metric late series 3 or a 2.5 any ideas please, as new rockers are needed.
The engine has engine number 36902300C it also has no timing chain but gears, believed to have been designed and fitted by Zeus engineering?
Thanks

is it metric or unf ,thereare only 2 types of rocker suffix c should be metric the later erc numbers

Thanks for that
Do you think it's original to the block?
The head takes the slimmer glow sticks