To use C-Drake with the SPR-4 the following is suggested:

A mod kit for the SPR-4 called the TA-4 was available to provide full transceive operation with a T-4, much like when an R-4 is used with a T-4.

You could replicate the whole thing or just the emitter follower portion highlighted in BLUE on the diagrams below.

(click above to enlarge)

TA-4 Schematic (click picture to enlarge).  Only the circuit in blue is necessary just to display frequency Connection to primary of T6 to the circuit above through a 5pf capacitor