Here is a quick early pontiac lesson.
1955-1960 pontiacs have the same rear bellhousing to engine mounts. This changed in 1961.
1960 pontiacs are not reverse cooled like 1955-1959 pontiacs. In order to have a perfect drop in replacement, 1955-1959 gmc or pontiac engine needs to be sourced.
The 1958 gmc 336 is based off the 1958 pontiac 370. The main bearings are smaller than 3 inches, and it has a shorter stroke than a 1959 336.
Find out for sure which motor you have. There are many more performance mods that can be done with a 1959.
The 455 has 3.25 inch main bearings and a 4.21 stroke. The 455 crank is not really compatible with a 389 crank due to the oversize main bearings.
Stroker cranks are available for the 1959 to 1979 pontiac 389-400 motors. A 1/2 inch stroked crank with a 0.030 over bore piston hole will make 447 inches. I believe a 0.060 overbore will make 453 inches but it has been a while since i did the math.
If stroking a 1958 pontiac block, the engine would have to be line bored for the larger 3 inch main bearings. This would be a good time to install 4 bolt caps. The machine work is not cheap.
I'm not sure about which tripower manifolds will bolt up to the engine. I know 1957-1959 manifolds will bolt up. 1957 and 1958 pontiacs used 3 small rochester 2 g carbs. 1959 to 1965 pontiacs had 1 small 2g in the middle and 2 large 2 g carbs on the ends. 1966 ppntiacs had 3 large 2 g carbs. Sometime after 1959, but before 1964 the intake manifold match up to the heads changed.
1959 pontiacs will be the easiest bolt in swap with an increase in displacement.
The timing cover will interchange between 1955-1959 pontiacs and gmc v8 motors. I used the 1958 gmc timing housing on my 1959 pontiac 389 because my truck had the rare factory power steering that bolted to the timing cover. The power steering pumps were relocated on 1959 pontiacs. Oil pans interchange between 1955-1958 pontiac and gmc v8 motors, but 1959-1979 pontiac v8 pans will not interchange with the 1955-1958 motors.
Butler performance sourced all the rotating parts for my 1959 pontiac 389 which was bored .030 and stroked to make 447 inches. I used a 1957 pontiac tripower that i had got years earlier with some other gmc parts. The stroker kit came as a ballanced kit with new rods, ross racing pistons and the stroker crank. I used a forged crank, but cast cranks are also available and cheaper. The block does have to be clearenced for the stroker crank.
My 1958 gmc flywheel had to be bored out to fit on the 1959-1979 stroker crank.
