[Unit 5302]

The kits come with special length lifters because the lifter bosses are deeper in the HO roller block. The cam bearings are also different.

Classic Trucks article on small block Ford

221/260/ Early 289

Although the 221 served duty as a reliable grocery-getter and was never known as a performance engine, the 260 and 289 engines changed how small-block Fords were viewed, first in the Falcon Sprint and later in Hi-Po Mustangs. These early engines can be identified by their unique five-bolt bellhousing pattern.

Late 289/302

The small-block that solidified Ford's reputation for performance was the Hi-Performance 289 4V. Produced from 1963-67, its distinctive idle, and the cacophony of its mechanical valvetrain coupled with ferocious rear tire shredding potential, made its presence known. However, of all the small-block engines Ford has produced, the most popular and frequently modified are the 302, or the 5.0L, small-blocks.

Introduced in 1968, the most desirable of these for street rod use are the hydraulic roller tappet engines. First seen in the '85 GT Mustangs, roller blocks have taller lifter bosses, and the cam bearing bores are bigger to accommodate the shaft's larger diameter bearing journals and base circle. But the real icing on the cake came the following year when electronic fuel injection was added. Unquestionably, for street rod applications, these are the most desirable of the Ford small-blocks.