I also want to update my 74 145 to a better interior, and have found a few things to consider. I had a 73 with vent wings, which your 164 may also have. The interior front door panels have a slight dip under the vent wing. The old style chrome window winder handles are much more durable and attractive than the newer screw on plastic ones.

Swapping of seats whould be pretty easy, since the cars have roomy interiors. I put some old 240 seats in my 145's and managed easily with minor modifications. Just bolted the new seat to the original seat mount bar.

At this age the plastic on the panels is somehat faded and probably brittle, so I'm seeking the newest panels that come close to fitting, and will trim and modify them to appear correct. The clip systems seem to be the same.

I have additional work with the carpet in the luggage area, but that has nice metal edges and can probably be reworked easily, maybe even with pad.

I would stick with 240 style seating, rather than a 740 which is obviously a different generation. I like the later wrap headrests, which actually give you a notch to settle into.

Best thing to do I guess is park next to a model you think might fit and comparitively measure things out. Some has to have a 240 somewhere you could look at.

Keep your findings (ha!) posted. Lots of engine performance talk here but not too much in the organic performance vein.