Question about used differential I bought
 

This is from mbz parts in Oregon. They don’t have mileage on it, but check end play and bearings. I have gotten good parts in the past from them. This is for a 82 300d with a 3.46
Any other indpections I can do before inserting or is it best to go to a shop and have them open and inspect. This would add a lot of expense

I don't have the answer to your question, but a thought about ratio. Is your '82 300D a turbo OM617? If so, shouldn't the rear diff been a 3.07? The 3.46 was non-turbo 5 cylinder.

if you have the differential on hand, at a minimum, I would suggest you drain/change the fluid and inspect the old fluid for signs of metal shavings/particles. If otherwise good, you'll at least know the state of your fluid. These diffs are very robust.

The car is a non turbo, that’s why the 3.46

X2 on checking the ratios and oil condition. Pulling the cover won't tell a lot more visually unless it's really bad. If the oil looks good without metal flakes, no funny noises or glitches whilst rotating it on a bench I vote for putting it in and hoping for the best.

Did you get the matching speedometer as well?

I do have a 2.88 from an 85 300D with matching speedometer I am not needing anymore.

How would a 2.88 drive in a non turbo 300d?
My car is a euro model with us speedometer and bumpers required upon entry to us.

Car currently has a 3.46 in it.Replacment is also 3.46. No need to change speedometer.

I had a very nice euro non turbo 300. That car had a five speed and a 307. Is yours a stick or auto? Mine would run 100 either in fourth or fifth gear. It drove nicely and if not too fast would do a tank making 40 mpg. My daughter had it at Ball state in Muncie in and mainly drove back and forth to Lafayette. The motor had been rebuilt and ran like a sewing machine.

The taller gears will make the car noticeably more sluggish on acceleration but will run fine in urban traffic.

It’s an auto and does well with the 3.46. Can do 75 with comfort and has good acceleration

awful. absolutely awful. Don't do it. Pros: quiet slow running at freeway speeds.Better mpg. Cons: can't pass or accelerate, more stress on the tranny. 3.07 would be better but these cars are so slow with poor acceleration.