Following up on this - had a blast all summer long on this setup. I took the car on multiple road trips across the rockies, plenty of hard pulls. After fitting an AEM TRU-Boost the car's been even better. The boost comes on so hard and fast, way more fun than stock twins, lag is not an issue IMO on the factory auto, and I put the entire thing together with decent parts - cast mani, turbosmart wastegate, fabricated downpipe, etc. for just under $2K CAD. This turbo size works perfectly for me with the factory trans and stock stall - I notice very little additional lag driving this on the street. Low RPMs and partial throttle feel a bit lazier, but lean into it a bit more and it builds boost and wakes up ASAP.
Zero issues, and I've driven it on cruises, road trips, and beat on it as well - not a single issue. Boost is controlled fine as far as I can see on the TRU-Boost with the cast manifold and 38mm gate. Full boost is coming in around 3100-3200rpm and I can hear the wastegate crack with my open dump.
Looking into which engine management to go with over this winter (AEM V2 came up cheap locally), and how to best control the factory trans. I'll be upping the fuelling - pump and injectors and want to properly tune the car. I was thinking MAPECU 3 but locally people are advising against it. What has been recommended is running a standalone in parallel with the stock trans ECU. Standalone controls the engine, but the factory ECU is there to run the trans. I'll update with what I go with. Goals are remaining at sub 600HP (realistically a solid 500HP is great with me).
I also have a transformer shift kit to install over the winter to help preserve the trans, I already installed a trans cooler when I first got the car.