Generally speaking, older rack-mounted TBCs like that were never designed for analog-to-digital conversion, but rather analog-to-analog editing.
The main problem is that "TBC" is a loosely defined term. There's TBCs, and then there's TBCs. Digital inputs need a frame synchronization, however most rack units were designed for genlock. Genlock and frame sync aren't the same. In Europe, the PAL CTB-100 TBCs are most often suggested and used, though there's been an issues with faulty chips in recent years. The DataVideo gear is also suggested, though harder to find in EU (even though it's PAL compatible).
I' hoping that some of our European members can add their input. Paging Goldwingfahrer.
That all said, I am aware of at least one VHS-to-DVD business using it. However, I've never seen their work.