My question is can I purchase this property, renovate the top two units and just leave the basement as is?

One of our biggest clients plans on building more up there and meeting another GC or two would certainly make sense.

An investment forum would be better for this post.With that said let’s look at these two but also let’s look at Risk adjusted.  

If you have units to remodel and are updating you can offer the senior tenant to move to the nicer unit and raise the rent, you can incrementally raise the rent, or maybe you can rent the other two for above market to make of the cost of the senior rent.

Quote from @Sean O'Keefe: This company is 3x the price of two well-known companies providing the same service and mentioned here:  https://www.biggerpockets.com/forums/51/topics/1136752-expla...Hopefully price isn’t the only consideration 🤔 For DIY, I'd say it's at the top of the list.

Purchase price: $290,000 Sale price: $72,500 Two-story duplex, each unit with 2BR/1BA.

Third is LOCALITY of service, the provider being a "local" provider. 

To make it easy, you can't buy in an LLC unless that LLC has two years of tax returns or if you are buying in cash.

I hope you are asking two separate unrelated questions, because there's no point in doing cost segregation for properties held inside your self-directed solo 401k, save for some very rare exceptions.Some of the Bigger Pockets experts who operate reputable costs segregation companies are @Bernard Reisz, @Yonah Weiss and @Julio GonzalezSome of the Bigger Pockets experts who offer Solo 401k administrator services are @Dmitriy Fomichenko, again @Bernard Reisz and @Brian EastmanReach out to them and see if they can help.

This assumes there are no third parties who took an interest between the original deed and the new deed (think mortgage lender).