The crt diff cup uses the 8x16 bearings, and is a direct fit in the savage.
You can buy the alu cups from InnovativeRC. I would suggest you buy them in his ebay store. Items bought from Rob's ebay store is shipped out way faster than from his regular online store.
You can find them here.
The roto start backplate is not supposed to look like that. I have converted 2 lrp's to roto start whithout any problems.
It should look as in the picture below.... no raised area around the bolt holes.
If you want a metal backplate, the ones from the SH .28 6port - roto start version, is a...
Looks like you'll have a lot of fun with that sled!
Follow the link below, and you might find some useful info on how to mod it.
I know it is highly modded, but it sure rips!
Snowmobile vids and pics.
Nice looking build, but I think you will have a hard time fitting the Ofna 250cc tank on to the FLM plate. The flm plate is too short. When I did this mod to one of my savages, I made my own plate.
http://www.rcbasher.com/pics/amidtank16.jpg
You can also get a plate suitable for the Ofna...