2240 with 2250 tube.

[chinaboy]

I'm currently working on a 1377 and want to make a CO2 next.  Before I start buying I want to plan and have some questions.  I think it would be cool to have the 2250 tube on a 2240.  So the barrel and the tube would be the same length.  Can you just switch the tubes and front end cap and everything lines up?  Or does this not work? 

And, can a p-rod grip frame work with these tubes?  If it is do-able I would think of attempting it.  I know I read a few post last month on this yet is seems hard.      Or I would use the 1377/2240/2250 grip frame.  If I do go with the 1377/2240/2250 grip frame, which frame do I want that doesn't have the plastic trigger cover.  I want to polish this gun and do not want the black plastic trigger cover that is on my 1377 that I bought last year.   

Thanks for any replies!