I just converted everything straight to cm. Since bases are 1 inch diameter, they become 1cm diameter, 2 inch blast becomes 2cm diamter. In honesty though, if you had a full size table (which I do not alas) you could just stick with inches, to represent speed of vehicles and realistic weapon ranges. Or perhaps half inches instead of cm.
There was that plastic spaceship ruins GW used to do ((
http://1.bp.blogspot.com/-eN1mdp97-cI/VWhRodjWpnI/AAAAAAAABNA/Ky6-UHIDcA4/s1600/IMG_1096.JPG) I think from one of their starter boxes, ultramarines vs tyranids), I always intended to pick that up as a crashed spaceship.
I do intend to return to this at some point, the old GW models are not so inspiring and would like to start again with some Vanguard replacements. I'm happy with the muties, though some additional microwave muties would be nice.
The trouble with Gorkamorka is that I don't think the rules were that good. I thought that back in the day, and I felt the same playing one game with these (granted, playing solo). Seems to be a bit of a dice rolling exercise, you don't roll that many dice but you need roll high to damage vehicles, there does not seem much you can do to increase the odds of doing so, meanwhile either the vehicle sustains unimportant damage or is out the fight leaving the whole thing a bit binary. But I like the setting and Mutie Raiders are among my favourite GW inventions, these noble but corrupted ad-mec fighting a crusade against the greenskins.
If you can find inspiration within the rules then I'd be interested to hear about it. Personally, I'm tempted to port it to another set, perhaps Stargrunt II but with each model effectively being its own squad.