I worked at Buick engine plant from 1990 to 1995 and heard stories about 1964 Rivieras with 4-speeds but never an Electra. Another clue to being from factory might be how the whole for the shifter was cut out. An Electra would be easier to make than a Riv because it has same front floor and shifter as a Wildcat that got 4 speed. The Riviera stories stated that the shifter arm was welded up to get it to the correct angle since those cars were never meant to have stick shift. If you ever worked for GM you would know that if it was physically possible to build something it was probably built, whether on purpose or by accident and with engineering approval or not. Anyone who argues differently has never been on the factory floor. I have thought about putting 4 speed in my 70 Wildcat convertible with factory buckets out of a hardtop, but putting a 4 speed in my 64 Electra 4-door sounds like even more fun. Would go well with my dual quad and 3.42 posi out of 65 GS Riv. I'll never forget being at GS Nationals in late 80's when a Bowling Green local pulled up to show in mall parking lot with light blue 4 door Electra with vinyl top and what he swore was factory dual quads. Does the Electra 4 speed have bucket seats? That could be a clue, too, to see if the bucket seat attachments look like they came from factory. Would stock Wildcat shifter hit the bench seat?