What are some of the best upgrades for a 1998 polaris trailblazer 250 I'm thinking about picking one up but it doesn't have the rear swing arm but I have one I would install how hard is it to install a rear swing arm on this machine if I did get the trailblazer would it be faster than a Honda 250ex

 

Not that hard to replace,but you have to remove the rear brake caliper and the clutches and backing plate to get to the mounting bolts. Replace the bushings item 16 and 17 if worn as there the cheapest parts.Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse
As far as out running a Honda 250EX you'll have to find one to find out or others can on the forum can tell you and also on any up grades. OPT

 

Will a 2001 scrambler 400 swing arm fit on a 1998 trailblazer 250

 

Bushings and pivot bolts completely different on the 400 versus the 98 swing arm.Frame mounting holes are different also.

 

I know this would be a lot of work but would I be able to put the motor and transmission on the scrambler frame

 

You just answered your own question. Yes it would be some work as you would have to transfer your electronics and modules over to the other frame along with any fabrication needed especially on the gear case and engine mounting.Look at some of the videos on You tube. People have installed sled engines,inline 4 cylinder street bike engines in atvs,even jet powered sleds and atvs. Just depends on how much time and money you want to invest in it.