So I picked up a NIB MK3 22/45 target with the 4.0 barrel on it from the funshop yesterday. It was only when I got it home that I realized that with threading the end and moving the front sight back that the front sight would actually be touching the receiver. I also noticed that if I want to mount the factory provided rail I will only be able to keep the front sight or thread it not both. Any suggestions on what to do? Should I remove the sights and just use the rail with a red dot.  Am I fucked on keeping the sight and the rail or can someone like ADCO lengthen the barrel to make this all work out?

Sights won't be touching the receiver.  

Here's my gun which I had cut back to 4".

Mine turned out like this...


I eventually built this as well...

Nice!

Bot a MKIII or a 22/45, but a MKII.  I had mine cut to 3.5 and it looks great, in my opinion.  I would think that you could have the rail cut down to still install on teh reciever and fit behind or around the front sight.