Excellent! The deYoung has two 2.5v windings (blue, grey, blue-white, and grey-white), not used in the ParaSEX. They can be paralleled to power a 2A3, or used in series for a 300B. You have quite a rarity; the ParaSEX only used the deYoung transformer for a very short while, and only on export (240v) versions.
The output components are designed for the stereo SEX amp (one tube per channel). The primary impedance is 8K ohms, and the rated power is 2 watts; the choke is 50 henries at 40mA maximum current. These are lovely components; I have them in my own stereo SEX amp, but they are not well suited to a 2A3. Here are a few options:
* Use the output iron you have, to obtain maybe 2.5 watts, but very clean below that power limit.
The following possibilities use new output transformers and plate chokes:
* A 4000 ohm transformer and 50mA choke is used in the Stereomour. It would call for a modest reduction in the PSU voltage. We rate the amp 3.5 watts but you can usually get at least 4 watts from this arrangement.
* A 3000 ohm transformer such as the TFA-2004 or very similar BH-5, along with a choke rated 55-60mA such as the EXO-003, should give you 4 watts. My article "SEX and the single 300B" was in the November 1997 VALVE, v4n11. It can drive a 2A3 as well as a 300B but the plate dissipation is 18 watts - too much for an old-stock 2A3 but fine for the Sovtek and other "super-2A3s". I used it for several years, and preferred the 2A3 - I used cheap Chinese biplates which were cheap but lasted 1000-2000 hours before becoming noisy. They sounded better to me than the Sovtek 300B. YMMV. You can reduce the plate voltage with an added resistor/capacitor to get to 15 watts dissipation.
* The Paraglow direct-coupled circuit is also a possibility; it ran at 2500 ohms and was rated 3.0 watts. You need an EXO-35/36 output transformer and a 60mA choke as above. The "soft-start" Paramount upgrade is a place to start; it can be used with many dual triodes including the standard 5670 and the 6SN7.
So, some food for thought. :^)