If I get the Midlength Base Upper, then buy the Samson EVO handguard separately, will I be able to remove the piston gas block to fit the handguard on? (or is that even necessary?)

Reason I ask: I might be able to get the Middy base upper and a separate EVO handguard cheaper than getting the EVO Middy base. Also, I know the factory uppers are pinned, instead of bolted. I just want to make sure I'm not stepping off a cliff when I go this route.

jncryer,
you will have to revome the gas block.  check out the video on the samson webpage.

http://www.samson-mfg.com/ar-15_html/category/Samson_Evolution.html

the following is opinion, feel free to ignore.

after shooting and building several version of AA piston kits, a one piece rail will cause issue with cleaning behind the gas block and under the rail.  the carbon and gas vents directly behind the gas block and that area can build up significant amounts of crud.  with a one piec rail system, you will have to remove the gas block to clean this area.

je suis de crackpot,
fatkid