The toploader shifter bolted on close to the front of the tailhousing, as I recall. T-5 shift tower is farther back? So you enlarged the opening rearward?
How I wish the T-5 had been available when I got my '65 brand new with High Performance Option, August, 1964! $3150.
S/N 5F07K284486. I adapted a big B/W overdrive to the toploader by making an adaptor and slicing off the tl output shaft and welding it to the O/D input shaft. Ask for pics, if you like! imps
Toploaders actually bolted on very near the end of the tailhousing. As you can see in the picture above, the T5 shifter is at the very front of the opening, and off to the side, as the Toploader shifter was on the side of the tailhousing. For the factory T5 shifter to fit required removing about a quarter inch of material from the front and passenger sides of the hole. I've considered moving the engine back, since I have an aftermarket suspension with a K-member that has 1" rearward mounting holes, but that will make removing bellhousing bolts more difficult, and I'll have to shorten the driveshaft as well. And modify the exhaust. But that's a project for another day.
Proud owner of a '65 289 coupe. Equipped with Edelbrock Performer intake, Quick Fuel 680HR carb, ported stock heads, 282 Magnum solid cam, Hedman longtube headers, MSD ignition, and decked and ported heads. T5 transmission with hydraulic clutch. Griggs Racing GR350 suspension. 8.8 rear end. Griggs front & Wilwood rear brakes. Many more mods to come!