Years ago, I was quite involved with a group of QSK operators, one was Dave W4AX a retired Western Union Wire Chief from NYC he improved on a classic design that everyone in the group used because compared to other units, this one was fool proof and if it failed, no damage would be done to your equipment.

https://archive.org/details/w4ax_qsk_box_1975-08-03/mode/2up

The PDF for this is here: https://archive.org/download/w4ax_qsk_box_1975-08-03/w4ax_qsk_box_1975-08-03.pdf

W9TO, Jim Ricks, W4AX, Dave Shafer, W4ZMQ, Marvin Carter, and others all used this and it was excellent.  They used it with Alpha amplifiers.

I think it could be used with transceivers that have a "separate antenna input" - or perhaps it could be modified for transceivers - 1975 we were still using separate transmitters and receivers if we were serious about CW.

73
DR