I free recommendation is to burn off the leg stubs. Have
a new base plate fabricated from 1/2" steel plate sized
to match the dimensions of Rohns pier pin plate. Find a
1 foot top section of your Rohn 25 that is still
straight and not warped so it will mate up with a new
section. Have the 1 foot section welded to the new plate
to use as an attachment pin like the pier pin base.
Have 3/4" hole drilled in the base plate in the 4
corners a minimum of 1" in from the edges and drill and
epoxy grout in 4 - 5/8" diameter threaded rods that are
embeded a minimum of 5 inches into the concrete base.
This is from the Hilti catalog and is the HVA Adhesive
anchoring system using HAS rods. The resulting system
will have 13,000 plus pounds of shear capacity. Since
your tower is guyed there is basically no moment at the
base to worry about and the plate being sized as the
Rohn pier pin base will be adequate for the compressive
load from the tower.
This is all based on the assumption that your new
installation will be the same as the old.
Actually you could use 1/2" diameter HAS rods also, with
5/8" holes in the plate.
Look up your local Hilti supplier in the yellow pages
and talk with them.
I concur with all the other suggestions that you use
epoxy anchors to reattach to the existing base.
Hank Lonberg, S.E.,P.E.