So I recently came across this from a seller whom had parted out a '70 Cutlass that had this straight tach unit in it (first image) - seeming to have been a privately commissioned reproduction without the OEM Tic-Toc portion (3rd image). My own guessing on its origin (the seller had no idea) led me to think about the repro '70-72 Skylark tachs that are commercially available thru several vendors, and upon which I'm wondering if this Olds creation was loosely crafted... Thinking this would be a cool piece to commercially reproduce if enough interest were out there (albeit no clue what vendor would take the project on)...

Interestingly, the 2 lamp socket pigtails are actual GM parts (p/n 8917345)

 

That is a nicely-done tach. It matches the speedo style well and has an rpm scale suitable for an Olds, not a Chev. Some of the details make it look commercially-made.

I wanted one like that but was not able to find any. I had a local instrument shop make one out of a clock.

 

Yours is done very well.

The one I noted does seem to me like it was based on the Skylark tack for its template just by comparing the general font type, numeric positioning and display color similarities.

I like however, that yours displays a static numeric layout across the whole range, would seem less confusing at first glance.

 

I believe gm sports salvage is the place that used to sell those tachs.

 

Gary VC455 that is beautiful and the same thing Ive considered having done. (But a '68 version with no clock)....
These pics are not of one I have - just adding them here because they are pertinent - I dug into this same question of OP about a year ago and that's why I saved these pictures. I never did get to the bottom of it, as to an answer what company made it/them..
But I believe I remember coming across something that one of the aftermarket vendors used to, but no longer does.
(I personally don't like the clock because it covers too much of the tach needle, but still wanted a "visually close" match to factory Olds design - ie: not a typical aftermarket Sun tach etc)
I'll be following along, down this rabbit hole lol

 

Restoparts was the company making these (item # BL00570), but they have been discontinued for a while now. Summit still shows the listing on their site:
https://www.summitracing.com/parts/o...grc8Qf4lFugFm_

 

I remember these but this one I recently came across isn't one of the Restopart models - it's almost definitely a custom made unit at least as far as the face display. The guts are probably a stock repro unit mechanism, I still think probably similar to the Skylark units

 

Correct. They have been out of production for a while now. There's a member here who's been looking for one.

 

Update - I installed the tach, still not convinced it's a Restoparts product given the marked difference in the display face compared to the previously advertised unit images available for comparison, but it does seem to work accurately.

Downside, backlighting is pretty poor - strictly around the perimeter of the face as opposed to the display markings themselves illuminating. I installed some LED lamps to help with that.

 

Looks good. The reproduction gauges and tic-toc-tachs have poor lighting as well. The main problem is that the inside of the housing and back of the trim ring behind the lens are not painted so they do not reflect the light like originals. If you can take it apart and paint the inside with a light blue/ aqua or white, it will likely make a huge difference.

 

Back around 1980 I stuffed a Sun Super Tach II in the clock opening. Its lighting is as bright as the factory gauges.

 

This is the tach I had been using until now - I cut the middle out of a clock delete plate to mount it - I'll keep it in reserve to put back in if the current tach fails.