Bob, Danny, when I did this exercise in 2013 ish the 3.0 was 58 pounds more and barely an inch which is why I was thinking about it. I saw a video of a Ghia with one... quite the engine. To get one fully rebuilt though was not inexpensive.
IM at the time, was pretty much doing 4cyl N/A or turbo's and I wanted the boxer Subie engine. I eventually went with a 175 hp 4 cyl and I wanted a subie tranny but I chose a 915 tranny like Marty. In the end, we went with a subie 5 sp.
As far as the pendulum effect in a rear engined car, IM builds probably the most stablest car with a 6cyl P engine car.
The physics in and of itself, cannot be trusted to not have a pendulum effect should it lose traction. Any rear lockup, or corner where you would lose rear traction would cause the weigh shift to swing the rear to come around.
Trust me, I know this from experience. I also am aware that Tomm had his car crash when he lost control in the rain? I believe it was partly due to his 340hp engine causing the rear to break lose. I could be wrong on these facts.
Am I thinking of upgrading my 2.5L today? No, but if the engine were ever to have an issue it would be part of the consideration with of course the 4 cylinders versions.
The tech guys that I have built a relationship with that are close to me could handle any engine choice I would make, and could fabricate anything that would be needed to do the conversion as well as tune that engine to peak performance.
Bob I really like my car!
Truth is, It was quite the journey to sort it out as I was the first full subie build. That means a lot of R&D and fine tuning. It was frustrating at times and very time consuming, I did a whole lot of trouble shooting and investigating of issues and I had a whole lot of fun and satisfaction especially when we finally figured it all out.
In passing, a lot my R&D done with IM ended up in the IM product line that was built after my car. From dual rads, thinner fan used, bigger gaz tank, and bigger gas filler, finally a microphone made as a button for the retrosound. Obviously as you help source out different things IM does it's job of building what you want and they did a bang up job.
IM has continued to improve the line and it's offering making the rad install even nicer as they go on.
I finally got my car singing quite well, and have made use of the original ECU wiring. Thanks to IM, and a close friend, who is an electrical engineer, who helped to finally decipher how to install all the needed stuff for a cruise control. This was quite the project doing it mostly myself but as of late, I have been able to do a lot of highway cruising relaxed with cruise control. Brings it to a whole other level of comfort.
Carlisle will be a much more relaxed 6 hour drive.