I always wanted to put an internal spring reverb into my Hi-Tone (Hiwatt DR102 clone but, I was never able to find any kits that accomplish this.
I even asked Hi-Tone to do it, and I offered to pay extra, but they declined.
Schematics, for Fender and Sunn amps are all over the net and sourcing parts and building the reverb circuit isn't too difficult.
As you know, the issue is doing the necessary math and designing the circuit update, to make it work.
You're talking about several days of work and no one (who is capable of doing the math and design) is going to do that for free.
Additionally, even if someone works it out on paper, there may be additional diagnostics/adjustments that wlll have to be to be made, once the unit is soldered in place.
There are a few guys at GAB that have the ability: Racing, Zozobra, Greatmutah, RiffRaff, FourT6and2, Mortatone and one or two others.
You can try sending each a PM. They are all nice guys but, you'd be asking a lot of them.
The next best thing is to get one of these:
https://reverb.com/p/fender-reverb-unit ... id=6357918If your amp shell has enough room, you may be able to put the Fender Reverb tank/circuit inside your amp, by attaching it to he Guitar input jack and powering it off the amp's mains.