Are these GM performance vortecs?

[racer1355inpa]

Wandering if GM ever made a set of performance Vortec cast iron heads with angle plugs. I came accross a set that have "GM PERFORMANCE" scribed on one end of each head. I can't find any casting numbers at the usual locations though. They are angle plug and have the tapped holes for centerbolt valve covers as well as the conventional valve cover holes. Anyone know?

[dirty white boy]

sounds like a bow-tie vortec

[stockcar5]

vortec bowties have straight plugs

[DaveBauerSS6]

Post pics.