Getting a repo horncast to fit

Just in the process of doing a dry build on a serveta project I've got slowly burning away. I bought a repo SX horncast off fleabay a couple of years ago and surprise surprise- its not a great fit, the bottom two bolt holes are a country mile off from lining up with the legshields . Anyone got any good tips for getting the bugger to fit? I know it's going to involve heat but I don't want to nuke it too much and be left with a blobby mess
ta muchey Paul
