I know that someone managed to get an arcade Namco recoil gun working with the ps2 guncon innards according to this video:
Basically, he wired up the 3- pin sensor and trigger buttons to the inputs on the guncon pcb and had it working well with a ps2.
Going off of that, you could probably use that setup working with a pc (though better with 3rd party innards) with Wingun, Guncon2PC or my eventual Topgun driver workaround.
In truth my end project I've been working on (while crazy as all hell, it's actually having moments of sweet success!) is going as follows:
1. A gun phototransistor/sensor cut out (while still mounted on part of the pcb) from one cheap-o guncon2 clone. I tried desoldering two of these things so far and forget it, they are SUPER heat sensistive. I opted to just cut a piece of a the pcb with the sensor on it.
2. Taking that sensor and mounting it in the barrel of this gun which is *basically* a knock-off of the namco arcade guns in design and solenoid...
http://web.cs.wpi.edu/~gogo/ps2_io/realarcade-superjolt.htm3. Running trigger wire and the 3-pin sensor wire over an old cut up lpt cable into...
4. A madcatz ps2 gun (like this one
http://www.lukiegames.com/PS2-MadCatz-8288-Light-Blaster_p_22024.html) taken out of the plastic and put into a project box, purely used as an 'interface' under the hood. I desoldered the existing sensor on the gun and wired in my previous 'sensor on a pcb' over the lpt cord. I can actually recommend the madcatz gun for superior tracking ability as a base, but the built in trigger feels pretty terrible.
5. A 555 and mosfet circuit living inside the gun, firing the recoil solenoid.
6. Crazy as it sounds, this mostly all works so far. Still working on the flash delay circuit for the topgun driver though.
How many pins does a happ sensor use? If it's at all similar to the namco arcade sensors (using a ~5V pin, ground pin, and what I assume is a sense/data pin) using a Guncon's board as an interface for the sensor could actually work. Maybe even an actlabs gun pcb could be a host for the sensor but I'm not courageous enough to hack those things being so rare and all.
As far as drivers go: out of the box I definitely had the most luck with Wingun as opposed to Smog's Guncon2PC because I couldn't get the screen flashing in smog's driver to work reliably, under 32bit XP Wingun was very good and allowed reliable flashing for games that needed it like the PC House of the Dead games. I use a jpac and soldered a female rca connection on the composite sync output line to my my monitor and plugged the guncon into that, and I was in business.