/6 was slanted to accommodate low hood on the Valiant and Lancer first version. There is no way it was done for distributor need as it was well down the tight side but it was well adapted for its location there. Length was shortened by the offset water pump but it still was a front heavy arrangement in that body. Also runner lengths were much more equal with the carb moved away from the head.Because most car and SUV buyers don't want an engine that intrudes into the cabin, or a long hood.
There are solutions. The staggered cylinder bores is one, and the Hurricane’s block is another, with even the cylinder sleeves taken out. The slant six was borne of the need to cut length; the slant made room for the (now obsolete) distributor and such. (I'm pretty sure it wasn't a height issue, Willem Weertman made it clear they'd only had room for a four cylinder. FOrtunately slanting the new straight six engine, by allowing for side-mounted distributor and such, was about that length.)