Well it is a 63 topoiler. The "HP" was very common to see on the 63 427's and it was dropped in 64. The 390HP was the first block to get the HP identfier and then the 62-63 406 and 63 427's. You should also see it on the back of the block, inside by the cam bores and inside the lifter valley. It should be a solid lifter block with the
oil pressure releif valve above the rear cam plug. The crossbolts look odd as the original were castle nut bolts. Possible they were swapped at some point tho. I'd ask to knock out a freeze plug to verify it has 427 cyl wall cores inside and drill bit test it. Some 406's were cast with 427 wall cores tho. So anything is possible. My C3AE-D 406 block was cast with one set of 427 wall cores on one side... and 406 cores on the other. Do you know what bore size the block is??
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