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I'd be just speculating, but after looking at some images / info, it appears as though maybe the t-stat housing only has 2 holes for two bolts.
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059 Manifold, intake 10052951 - -
060 Stud, hex (3/8-16x1. 24, 3/8-16x. 75)(#1 rh) 00336793 - -
060 Stud, intake manifold (3/8-16x0. 78)(#3, 4, 5 lh)(#3, 6, 7 rh) 10085606 - -
061 Thermostat, (195 deg)(acdelco #131-87) 12514334 - -
062 Gasket, coolant outlet(acdelco #10105135) 10105135 - -
063 Outlet, coolant(acdelco #15-1461) 10126717 - -
The above info comes from here (after searching that part number you provided).
Parts catalogs. Spare parts catalog Chevrolet EPC Online. Chevrolet K1500 PICKUP 4WD. . Engine asm-7.4l v8 part 2.
nemigaparts.com
The intake imaged way up top is from a old ebay listing, best I can tell.
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A pic from ebay of the part number listed by nemigaparts.
Makes me wonder whether the t-stat housing bolt holes in the intake there are exposed to coolant / passages. Like if you only used two bolt, would the others two holes leak coolant.
Hopefully others here have better, more definitive info for you.
Best of luck.