Not sure which ones you mean, this is what I see for front piston sizes for Cadillacs:

04-07 CTS-V - 40/44
09-15 CTS-V - 30/34/38
16+ ATS-V - 30/34/38
16+ ATS - 42/42

PP is 40/40

04-17 STI - 40/46
18+ STI - 30/34/38

The only thing I've really found that matches the PP 40/40 is the FK8 Civic Type R, but the bracket shape doesn't seem right (disclaimer: I haven't measured).

Also, thank you for making me double check, I typo'd the STI front pistons in my other post.

I had a set of these Rockauto ones powdercoated red to match PP.

https://i.imgur.com/WxZsa6e.jpg

oh, odd

https://www.ft86club.com/forums/showthread.php?t=117769

this says the front brembos are 42s

further research looks like 40s though, but his brake calc with ats front and evo x rear (same size as sti rear) puts bias close to stock.

The below are 38/42 brakes:

ACURA

TL: 2004 - 2008
AUDI

R8: 2008 - 2012, 2014 - 2015, 2017 - 2018
DODGE

Viper: 1992 - 2006, 2008 - 2010, 2015 - 2017
FERRARI

360: 2000 - 2005
NISSAN

Sentra: 2004 - 2006
SRT

Viper: 2013 - 2014
VOLVO

S60: 2004 - 2007
V70: 2004 - 2007

Alfa Romeo Giulia 2.0 also has 40/40 brakes. The caliper seems to be a monoblock which would be good. Not sure about offset and adaptor bracket (rotor is 13” instead of 13.8”)