Its quite a simple proceedure buddy if your good on the tools and have time to spare and take your time. Best thing is to make sure 100% you have everything on site and ready laid out before starting the job albeit the most cheapest option would be to change vehicle buddy to an auto. Not ideal as you mentioned you had a lot of time and dosh invested in your current ride but sometimes you have to bite the bullet and take the easiest route.
Its not as easy as you'd think. With the P38 there's a whole load of electrics to deal with. It's trying to get them to work with the existing loom. I'm brilliant on the tools, but getting the electrical side to work will be fun. I've considered buying an auto but they're either ropey or silly money.
If you were closer you could swap over with the autobox in my scrapper. That would leave me a spare manual box.
However, I think you would do better looking for an HP24 box out of a 4.6. you'll need new props as well though and the gearbox ECU and maybe even engine ECU as I am fairly certain the auto ECU was slightly different. Obviously there's the different gear-shift too. And then you'll have to chip it to stop it feeling sluggish. All in all, easier to stick with the manual and take up squats and deadlift.
Thats the plan. Rebuilt HP24, ashcroft modified torque converter all mated to the HP22 bellhousing. I can source all the bits from an auto, its whether or not it will swap into mine with minimal wiring changes. The only solution would be to run a hydraulically controlled HP22/24 with a kickdown cable. No wiring involved and the most robust setup. The only thing is i'm not too clued up on the hydraulic HP22 or how to make one work, nor will ashcroft tell you anything other than they can build you one. I'm already running a chip, straight through exhaust, hybrid turbo with an electronic boost controller.
I ended up fitting the mild uprated clutch instead, I fitted the HD unit but the pedal was horrendous. It would have ruined the car for me.