My first suggestion would be to abandon your plans with the Hasbro saber and pick up an MPP 2.0 from Korbanth or TCSS. It would be far easier in the long run. There are tons of little things you have to work around when doing conversions and it'll try your patience. The MPP 2.0 was designed to be a buildable saber.
You can't use the shtok switch holder with the Hasbro, unfortunately. Or pretty much anything else made for an MPP or 2.0. If you're determined to do a full conversion then there's an MR chassis on Shapeways. You'll have to look for it because I'm not sure if I can post the link, sorry.