I bought a bunch of Cast-A-Way swivel arm bodies when these Mattel figures hit the stores and if I remember correctly, there was very little effort to get the Mattel heads onto those bodies. I don't even think I had to Dremel out the neck holes, but I may have had to just a little.
If I were going to transfer a Mattel head to a "Mego" body these days, I think I would snag a Type S body from Classic TV Toys/ Figures Toy Company for $10.
http://www.classictvtoys.com/typesre...hmalebody.aspx