Wiz and 'specially the OP,
The rads are cool bikes and we have a bunch of them here in B-town. So so saving yours is gonna be a good thing.
Wiz, Yes the last 35 years in the golf repair industry has taught me a bit. And I have a bunch of white papers and mag inputs which has made me well aware that I need a transciptionist to help me out with the printed stuff that comes out of my mind. But here on the forum I'm "on my own in the wild" so to speak.
Now epoxy bonding: .005" is the optimum for adhesion .010" is an outside limit even with glass beads used as filler to help keep the epoxy from becoming the matrix to hold everything together. So yes a good bonding between a new steel sleeve for a seat post and the old aluminum seat tube is a must. But as I see it, a steel sleeve post epoxied in about two inches down the old Al tube will be a good solution. Cut a relief in the top of the steel post for a clamp and install a new seat post. Any BMX post clamp should work and a 1" BMX post would help make the rad bike even more rad! Just again my opinion, but it will save the bike and make a $1500 bike ride-able again. Smiles, MH