First the good news. What you have builds into a useable gas turbine in a days work producing about 14 lbs thrust. I believe the mk 3 was one of the later ones. The box you have cost about 1800 $ It has significant value even as spares as there are a lot of the old Wren 54s still in use.
Not so good news This is from the Wren web site
Homebuilders
Supplies for homebuilds from the Wren plans are now exhausted.
The designs in the plans are over 14 years old - design & technology has moved on so far/fast that current engine parts are not compatible with those from the plans.
You should get at least $ 500 and maybe as much as $800 providing everything is there and untouched.