All depends on your purpose. I would love to have that YT block as I have two '68 Firebirds and neither have their original drivetrains. The $1,500 might make sense if someone was doing a concours restoration of a a '67 400 manual Firebird, to anyone other than that probably not.
'68 YT blocks are difficult to find, getting for $450 was a good buy.
1968 400 Coupe, verdoro green, black vinyl top, auto 1969 GTO Judge coupe, Carousel Red, manual 1971 Trans Am, cameo white, auto 1970 Buick Skylark Custom Convertible 350-4(driver), Fire Red, white top, auto 1972 Buick GS Stage 1, Royal Blue, black vinyl top, auto