Hi Phil
For trying to answer your question :
On my two "modified" Binson, I kept (as Didier

said) the original wheel (or drum) BECAUSE it's the same "system" of recording/playback than an SEP (F, J or Vox Echo)
Now, and as I tried to explain in my last post :
1) I can't explain why with the same electronics, the "density » and the mix of the four delays composing the final halo of reverb could be different between the one found (got !) on an TAPE Echomatic Meazzi and the one found (got) with a Drum system ?
But if you can compare (and You and I were able to compare and say) SURE it's "different"...
2) The question (for me !) is to know, if the acoustic result (or the transfert curve) between the "coating » of iron oxyde on the SEP drum is similar than the acoustic result obtained with he iron wire wound on the Binson Drum ?
Compare with my tape Echomatic Meazzi the acoustic result I obtain with my modified « Binson / SEP /Vox Echo » (!) is "similar…
Just one more time the density of the halo of reverb is « better » with the drum than with the tape, and "acoustically" very near from the Hank SEP's one.
Nevertheless:
Like on a recording tape, the apparent running speed in front of the heads can also change this result…
Even if the different of the relative « speeds » found on an original SEP/Vox Echo, an Echomatic Meazzi or a Binson are « similar » or « near ».
But you can also understand that it's difficult to say that you can CLONE the response of an original SEP drum with the Binson one ?................
It seems ! Or I think...
But be sure, SINCERELY, that this kind of transformation done on a Binson is more than just (how i can say ?)... a "toy"
3) If somebody would like to transform a PE 603 (T or X) Binson into a Vox Echo i’ll try to give him the informations I know (or I beleive to know

) on this subject .
Keep in mind that, you have FIRST to choose (buy or try to buy...) an (original) TUBES PE 603 (T) Binson model to do this job. Simply BECAUSE the internal volume of a PE 603 permits to wiring with no problem

...and because you can use again its main transformer (6,3V for heating, and HT)
If you chose to do the same from a TUBE Binson Echorec, its inside volume is full like an egg (like we say in France…) and it's not so easy...
Best regards
Patrice