This is not a conversion that I did. However I purchased a 3000gt that had this conversion done. The 3000gt was in rough shape (rusty underneath, no motor, had been rear ended hard) so I ended up parting it out. However since the targa conversion was so unique I decided to take a lot of pictures and document what had been done really well. I ended up cutting off the entire top section of the car and selling it as a targa conversion package to a guy in Mass. He'll be putting it on his track car along with a full cage setup.
A long time ago a member of 3si.org forum discovered that by utilizing Spyder hard top components you could cleverly create a hard top out of a 3000gt. DustinP was the name of the username of this 3si member. He was able to acquire 2 wrecked Spyders. He pulled off what he needed from one of the tops and converted his personal 3000gt into a targa. Then he tore the roof apart on the other Spyder and made a targa conversion kit that he sold for $4000. I believe the car I acquired was owned by the guy who bought his extra kit. Here are DustinP's old threads discussing the conversion:
Here is a pic of DustinP's old car. Pictures of the targa converted car I acquired are further down.
There are only a few. There was this one that I parted. DustinP's original car is now owned by a member on 3si called 91red_stealth and it's still around. He has pictures on his website which can be seen here: https://sites.google.com/view/raeganracing/overview-1991-3000gt-targa-sold/exterior-pics What is interesting about the original design from DustinP's car is that the top bolted in. They didn't re-use the front spyder electric latch system like was on my car. 91red_stealth later changed the design so that it would use a latch locking system stolen from an 89-92 Mazda RX7 convertable.
Then there was Mitsubishi's concept car that later became the released 3000gt. Originally it was called the Mitsubishi HSX and had a targa top. I'm not sure how many concept cars were made and/or where they are. But they would have the targa. Jackie Chan even drove one in an old movie. You can find the HSX concept brochures on ebay and if you look closely at the center page, you will see the roof is a targa. There is another 3s member who also attempted making a targa without using Spyder parts and gave up when it came to trying to seal the roof.
This list should give you a general idea of what was initially involved in this swap. I also have a Youtube Video below it which describes it further.
Basically I cut everything off my targa converted shell so that it could be applied to a cleaner rust free shell. This was a proven solution that had been on the road for 10+ years.