Apparently the only part that's 100% compatible between the Delta Trooper and the Retaliator is the spring.  There are a few articles around the NIC from nerfers that upgraded their Delta Troopers with Retaliator springs.

But the mod sites like NFStrike, BlasterParts, and FoamBlast have very few parts for the Delta Trooper. Mostly just short dart conversion kits. For instance, when you use the site search at NFStrike for Retaliator, you get 190 items. Do the same for Delta Trooper, you get 10 ☹️  (for you math nuts, that's more than twice as many, twice, times two, then twice as many) 

As a non-Retaliator owner and a non-Delta Trooper owner and a long-time modder, I'm going to say No, things like the bolt sled and breeches aren't compatible. Sorry Butt-Ugly. Or is it Martian???

Thanks, and it's Butt-Ugly Martians