*Note that this isn't a genuine DACT attenuator, hence the seller's calling it a "DACT Type." It is a Chinese clone.
The attenuator is physically smaller than the stock Dynaco volume pot. Its mounting boss is also smaller than the hole in the Dynaco front panel. This is no problem except that you may wish to carefully align it in the hole before tightening the nut that secures it. You may want to get a proper-size lockwasher, to prevent the new attenuator from rotating or shifting in use, even if you tighten the nut firmly; only a flat washer is supplied. The shaft is splined, which matches the PAS-2 and PAS-3 knobs; factory-built PAS-2x and PAS-3x have nonsplined shafts and setscrew knobs, but their knobs work on the splined shaft, just fine. The length of the shaft is correct for the Dynaco PAS; no need to hacksaw it to length, as on the Radio Shack ALPS control, which is of the wrong resistance anyway (100kΩ vs the correct 250kΩ).
A locator lug on the attenuator must be broken off, as there is no matching hole for it in the Dynaco PAS front panel.
Note that the attenuator does not have a loudness tap. The loudness control on the stock Dynaco will not work; its wiring should be removed and the loudness switch bypassed.
The attenuator being smaller may cause some minor issues if the existing wiring is too short, as it's a longer "reach" for the wiring to the solder pads than it was to the lugs on the old volume control. I had to remove and replace the existing wires; they either didn't reach or were marginal.
It helps to prewire the attenuator before physically installing it to the front panel, as it is easier to wire up to the mode switch and circuit boards than to solder to the attenuator once it is in position. Be aware that you are soldering to printed circuit board material, not to solder lugs as on the stock volume control. When I prewired it, I took care to solder the wires to the REAR of the connection board so that the wires would not foul the front panel. as the spacing is close. Also you must make sure that the soldered wires do not short to the front panel due to being too long. Use nothing larger than AWG20 solid wire; larger wire won't fit in the holes in the solder pads, and stranded wire is a pain to get through those little holes.
On completion, the installation was a complete success. Its channel-to-channel tracking is very much superior to that of the stock Dynaco potentiometer and audio played through it is noticeably more "transparent" than through the admittedly old stock Dynaco part. The internal switches are "make-before-break" which eliminates popping sounds as the volume knob is turned.
Suggestion: while you have the preamp opened up, clean the rest of the controls and switches, too, using an appropriate product.