[rotorwrench]

The Whiz kids, or what was left of them, made decisions with some input by Henry #2 by the late 50s. Interchangability was likely close between the 259 series and the T86 since they were both light duty types but the heavy duty T85 is larger and heavier. A person would have to do some parts research on the available rear mounts & cross members for the 1955 sedans. The Thunderbird and Mercury applications were still considered heavy duty but there wasn't a lot of difference in powerplants unless a 6-cylinder was involved. The Ford sized Y-blocks were all close to being the same even if displacements were different. Lincoln and later Mercury were big Y-blocks.