First off, welcome aboard.
You can't tell what size the turbo is by measuring just the compressor cover or downpipe openings. You must take the compressor cover off and measure the inducer and exducer of the compressor wheel to know exactly what size the compressor wheel is. You also need to do the same to the turbine wheel by taking the turbine housing off and measuring the inducer and exducer of it as well, in order to know for certain what it is. However, removing the turbine housing on an older, rusted turbine housing is a real PITA and not easily done.
That looks like an E compressor cover, (3" inlet, 2" discharge) commonly used on TE44 and TE60 turbos from way back. It also has a cast twin 7 blade compressor wheel which IIRC was a TE60 wheel, but I could be mistaken. I also spy a 3" ATR downpipe with their external wastegate peeking out.
Here's some ways to check.
If it has a Precision turbine housing on the hot side, chances are it was made by Precision or Limit Engineering back in the day before PTE starting casting their own compressor covers, circa 2002ish. Here are a few things to look for.
Take off one of the backing plate clamps that bolt the compressor cover (cold side) to the backing plate. You are looking for these letters followed by two numbers, CCExx. So CCE44 or CCE60. Obviously CCE44 would mean it's a TE44 and CCE60 would mean it's a TE60. See attached photo for the backing plate clamp circled in red. Bolts are 13mm or 1/2" and are typically hand tigtened in a criss cross fashion when put back together. There should be 2 clamps. One that's 3 holes and one that has the wastegate welded to it. But in your case with the external wastegate, you might have two clamps, or even just some washers through the bolts holding the compressor cover on. Somewhere behind those clamps, will be the CCE numbers machined into the compressor cover but there might not be any because of the age and a Garrett cover.
View attachment 333189
Seeing that yours has an older Garrett compressor cover, those CCE numbers might not be machined into the cover, but it never hurts to check.
You can also look at the turbine housing and see what A/R number it has. It will either be .63 A/R or .85 A/R on a Precision housing. 95% of the time the E cover turbos have a .63 A/R for quicker spooling.
If it has a Garrett turbine housing, it would either be a .63 A/R or a
.82 A/R. The A/R number is located just above the 3 bolt header flange on both Precision and Garrett turbine housings. See pic.
View attachment 333192
If it has a Precision turbine housing, you can unbolt the downpipe and look on the turbine housing flange face for a part number. Precision machined a part number on their 3-bolt Buick housings that starts with THB. Meaning, Turbine Housing Buick. An example would be THB3-31 or THB5-52. The 3 means .63 A/R, 31 means a T-31 or Stage 3 turbine wheel. The 5 means .85 A/R and the 52 means T-350 or Stage 5 turbine wheel.
See pic.
View attachment 333194
If it is a Garrett turbine housing, the only markings will be the A/R number.
With that being an older turbo, the last ditch effort before removing the compressor cover and turbine housing and measuring both compressor and turbine wheels, would be to look on the compressor cover discharge for a hand engraved part number or model number. That's typically located here. See pic.
View attachment 333193
You're looking for TE-44, TE-60 or something similar.
Chances are, it's a TE-60, seeing that you had 50# injectors with it.
Spec'ing a replacement:
This has been a well worn topic for years, but is frequently brought back up due to turbo technology changing so frequently. All of the major turbo players are constantly coming out with new model turbos so it's understandable to see these questions brought up. Depending on your goals, there are a lot of combos that are out there now. The basic 6262 turbo with 60# injectors and what you have with proper tuning, is enough for 10's. If you were wanting to go faster and go with a cam swap to get the most out of those heads, the 80#ers and either a 6466 or 6766 turbo is enough for 9's with the right tuning, but those turbos need more converter if street driven.
It really comes down to what you want and your ultimate goals. As has been said numerous times before, 95% of the Turbo Buick owners never utilize what they have and go over board with turbo selection. Use the search feature and read up on the 6262, 6466 and 6766 turbo combos. Both Bison and PTE offer fantastic options for our cars.
Hope some of this helps and again, welcome aboard.
-Patrick-