And then there is Kugel Komponents - Reverse 90° Under Dash : Kugel Komponents, Quality Komponents Since 1969
As far as room, you have it with these Kugal parts.
BUT - why the desire for a 4-5-6 speed manual? An auto will shift faster, be more reliable and the exterior parts are more easily located, i.e. under the floorboards. Yeah, I looked at running a 5 speed in mine, but after spending a bunch of time going through what you are now, said screw it!! A well built C4 will do everything necessary (TH-350 with a Chebbie). Very happy I did as trying to move size my size 12's attached to my 6'4" body to three pedals would have been not a good time for me at every stop. Yeah, a coupe has a little more room then a roadster, but not a heluva lot more. Today, and knowing what I know now and since I built from scratch tho using a TCI Stage lll chassis, would have extended the frame beyond the firewall a few inches then used a standard firewall as the 5" recessed version wouldn't be hurting my foot room.
Whatever - it IS your car and choice, albeit a difficult project