50 Merc head bolts - two different types?

[Jack 34pu]

I recieved a large can of head bolts with my 50 Merc block. There seems to be (2 lengths - of course) two types. One type seems fatter and the other is thinner with an enlarged area near the head (same threads). Are they interchangable on the 49-53 heads?

 

[51 MERC-CT]

Should be interchangable.

There are two different length bolts.

1-15/16" and 2-5/8"

 

[52merc]

also 2 different bolts 1 has the same size shank up to the head of bolt the other is not like that it is thinner from thread up to head both work same also 2 different lengths