The heads had to be ARP'd and failures were high...that's why Ford finally gave up on it and just went with the 5.0 - much the same as the Mustang SVO with the 2.3 Turbo.
Ford didn't 'give up' on the 3.8L in favor of the 5.0L. On the contrary, the 3.8L (N/A or SC'd) outlived the 5.0L. The last year for the 5.0L in a Mustang was 1995, the Last year for the 5.0L in the `bird was 1993. The last year for the 5.0L in ANY Ford Product was the 2001 Explorer.
The last year for the N/A 3.8L was 2004, in the Mustang. The last year for the SC3.8L was 1995, in the Thunderbird..2 years AFTER they quit putting the 5.0L in them...
Almost every Ford V-6, (90 deg. and 60 deg.) seemed to be more prone to Headgasket failure for whatever reason...
And the fact they started Supercharging the `Birds starting in `89.....it didn't make things any easier on them....
And you need to learn some facts about the SVO program, and the 2.3T....Which car was FASTER? The SVO, or the GT from the same year? AND which got better mileage? Here's a clue...the answer is the same for BOTH.
And as for why don't more people use Tom's parts? Well, they are STILL overpriced and unproven in a 2.5 tonne (I spelled it that way on purpose) Daily Driver. And even if you were able to overcome those 2 HUGE hurdles, how many transmissions will you break before you realize that there is NO WAY to put THAT MUCH power to the ground using the standard array of transmissions available for the 60deg. Ford V-6...
TO ANSWER THE ORIGINAL POST:
Yes it has been done before....There is a whole write up on the build up on the internet somewhere. I have it saved on my computer, but I don't have time to find it right this minute. Very little fab work was required. Making a manifold adapter was the hardest part, and it just required basic MIG welding skills, and a 2x4 steel tube.
Ryan