Hi guys. :-)
Wow...this has gotta be my first post here in quite a while! I was just being a bit nostalgic, browsing through my old projects and stumbled across this.
TiM!, you're welcome to use my motor mount design if you'd like. The main thing with the Havoc is that it really needs the gearbox to be braced against the chassis if you plan to do any jumping or stunts with it, to prevent the gear mesh from moving and destroying the spur, so you might want to look into that if you decide to use a Revo mount instead. The Havoc is a great candidate for brushless conversion - one main reason being the the drivetrain is (almost) BL-proof with no messing around. You might find fitting everything in on the chassis can be tricky as space is at a premium, but it can be just-about done. With some shoe-horning, lol.
If you'd like any help or pointers, then feel free to shoot me a PM and I'll try to give you any help I can. I don't have time to check the forums much any more (my job is the only reason I'm out of RC at the moment - just no time for it!), but if you PM me I'll get back to you. If you want, I might even still have the CAD designs for the motor mount. I'll have to have a dig around for ya. If I can find it, I'll send it to you and then all you need to do is send it to a machine shop to get it cut.
Good luck with the project mate - it's great to see there are others still working with the Havoc!
And it's nice to once again post here...it's been such a long time. I hope everyone's doing alright. Hopefully one day I'll be able to become active here again.