There are guides and information on the site linked below on how to do your own halfblock:
http://www.halfcocker.com/modules.php?name=Content&pa=showpage&pid=5http://www.halfcocker.com/modules.php?name=Content&pa=showpage&pid=3There is also a lot of information in the FAQ about halfcockers including some places that will convert your existing body here:
http://www.halfcocker.com/modules.php?name=FAQ&myfaq=yes&id_cat=1&categories=Halfblock%2Fturtle%2Ffastback+cocker+FAQThis forum member will convert your existing marker for you for as little as $100. The service doesn't appear to include anodizing, so you would end up with bare machined surfaces when it was finished in places that were cut or milled. You can send it elsewhere to be anodized later, and it is the cheapest conversion service I have ever seen offered.
http://www.halfcocker.com/modules.php?name=Forums&file=viewtopic&t=343That said, my brother has a System X body on one of his many markers. We have found that the body doesn't conform 100% to standard autococker size and shape. The only real issue that we have found is that the barrel threads in the body are a little bit off, so some barrels don't fit while others do. You might want to consider buying a new body before conversion. Some companies will provide you with a new body for an extra charge. A new body also means that you wouldn't have to send in your existing marker meaning no downtime, assuming that could tear down and rebuild your own cocker.
A listing in the FAQ or the halfcocker forums should not be seen as an edorsement of a particular person or company. Do some research and ask around before selecting.
Further, attempting a halfcocker conversion yourself without the proper tools or know-how is potential for disaster. A finished-looking product almost certainly will not come from a hacksaw and dremel.
