[nize]

the problem with keeping it 'stock' is the stock wastegate costs $2821.75
https://www.pelicanparts.com/More_Info/95112301504OEM.htm?pn=951-123-015-04-OEM&bt=Y&fs=0&SVSVSI=1026

the tial 46mm is 'the best' one but most people go with the tial 38mm because it's a little cheaper. old threads are here:
http://forums.pelicanparts.com/porsche-944-turbo-turbo-s/389978-tail-vs-lr-dual-port-wastegate.html

and here:
http://forums.pelicanparts.com/porsche-944-turbo-turbo-s/383961-about-wastegate-spring-rates.html

and here:
http://forums.pelicanparts.com/porsche-944-turbo-turbo-s/1048045-wg-tests.html

*beware* most tials on the market today are counterfeits, be sure you are buying an authentic tial.
TiAL Sport - Spotting a Counterfeit TiAL
*11/11/2021 above link dead, new link*
https://www.topspeedparts.com/blogs/news/how-to-spot-a-fake-tial-mvr-wastegate

fake vs real how-to:
https://www.youtube.com/watch?v=__Jzk0XXvr4

fake vs real teardown:
https://www.youtube.com/watch?v=2nOPLxln5Ec

SFR has kits available and is a reputable company so i'm guessing they have real authentic tials:
Wastegate – Speed Force Racing

if you want to risk getting a possible counterfeit tial you can get the adapter for the 38mm separately here:
https://944store.com/product/944-turbo-tial-38mm-wastegate-adapter-plate-kit/