Welding the SD starter bellhousing cone to the Toy bellhousing is tough work. There is no provision to adjust the starter drive gear-to-ring gear clearance on either design, so positioning before welding is critical.
I read a few pages worth forward in that thread to see if he had problems with it later, but there are 113 pages in that thread, and when I hit the homophobic shit on page six I gave up . . . someone else will have to dig for the info.
It worked fine for him, he took that thing all over the country. However he did swap a toyota diesel into it later for more power. As I understand he built, or someone else has built more than one of those bell housings allowing use of the SD22 on a toyota tranny.
There is some pretty good stuff in there too, such as running a super charger on the SD22 and lots of turbo stuff.
It didn't work fine by chance; he had to have done a good setup job, that's not easy. Not a procedure I'd recommend to someone who doesn't have excellent layout skills.
Even aligned, it would still have to be faced (and probably bored) after welding, for long-term bearing reliability.
OTOH, an adapter plate might be fairly straightforward, at least for me. Maybe.