yea thats an aluminum block.
so far as the Teksid being a stronger block, some say it is, it was cast in italy and blah,blah,blah and its better.
but really, all the 4.6 blocks have proven to be very strong, alum. teksid's, non teksid alum's, and iron alike.
it really comes down to personal preference, and wieght. the iron blocks weigh 180 pounds, the alum. blocks wiegh in at barely 100 pounds.
if your looking to save wieght, alum. is the way to go. if you dont care, get whatever you can find. i dont think there is even one story of someone breaking a block because of to much HP. they are very strong. not like the old 5.0 blocks that split over 500hp.
im building my motor with an iron block. i got it because it was free, and everything was straight. picked it up for free, paid 50 bucks to have it hot-tanked and checked for deck smoothness, and all journals and bores for straightness. everything checked in well under spec.
i wanted an alum. block at first, but couldn't find any near me. so a free iron block for me.