‘59-‘60 water pump bolts

[David Greenburg]

I’m replacing an aftermarket water pump on my ‘60.  The mounting bolts all appear to be original, except for the two lower right hand bolts, which have been  replaced by new bolts which have the correct thread and shaft size, but have a 5/8” (socket size) bolt head, while all the other bolts are 9/16”.  Does anyone know if that is correct?  It may not matter, since there is enough clearance for the larger bolts, but if someone lost the original bolts and just shoved whatever fits in there, I’d like to get it right.

[Dan LeBlanc]

If I recall correctly they should all be 9/16" heads but only you will know the difference

[The Tassie Devil(le)]

Could they have possibly fitted Whitworth bolts in there?   These will fit in the thread department, but the heads will be larger.

Bruce.

[David Greenburg]

Dan:

It just dawned on me seeing your reply that I could have just looked under the hood of the Fleetwood to answer my question.  I don’t care about having the correct bolts just to be “correct.”  I just want to do all I can to minimize the chance of a leak when it goes back together.

Bruce:

That is a possibility. The pump was installed by a shop in Las Vegas that worked on the car after it overheated on the way to last year’s GN.  The shop was restoring some high end British stuff, so they might well have had some Whitworth hardware floating around.

[fishnjim]

Fasteners are also in the parts lists. 
I recall they're all the same heads just different lengths.   Washers too.
Sometimes water pump bolts corrode and you can't get the right length or proper finish, since they made half length sizes and non-bright plate back then, but just keep persisting.   Fastenal or local bolt suppliers can usually find just don't take the first no.   ARP makes different head sizes in some sizes.
You can take a modern bright plate and bead blast and they'll look correct.  But I believe these are painted with motor from the factory.

[LV 57 SEDAN DE VILLE]

Is it possible that the 2 bolt holes were stripped and tapped to the next larger size when the water pump was replaced? Just a possibility.