I am glad to welcome you to the forum! We used the Studer A810 model, received after restoration from the Swiss company Z-Audio (the work was done in cooperation with the Revox factory, which resumed its operation). For restoration, "native" spare parts were used, but the head unit was completely new. Each model from Z-Audio is also issued with a "report book" on the obtained measurements of the reel-to-reel recorder
This is a "new heads" form Flux Magnetic, but the recording and playback system is 2 tracks stereo 38 cm / s. Here is an example https://www.atrservice.com/flux-magnetics-tape-heads
Quarter-Inch ERP – 2-Track Stereo
Many R2R fans now using Flux Magnetic heads on A810/A80