The pictures you see on the B&H website are cut and copied from the manufacture website. It wiuld be the same product as seen ton the Trijicon website.

It is a type 2.

You can mount an RMR on your scope with BH #TRRM35. That is the part number you will find the RMR mount on the B&H website.

Yes, the lens covers are included.

The tritium can be replaced by Trijicon by sending the optic in to them directly.

I can only verify that the Trijicon 4x32 ACOG Dual Illuminated Riflescope and 3.25 MOA Red Dot Type 2 RMR Sight Kit (DI .223 Red Chevron Reticle, Matte Black) BH #TR4X32RC223 • MFR #TA31-D-100549 Mounts on ACOG and comes with Trijicon ACOG Picatinny Rail Adapter

By Fiber Optics.

The problem is one of velocity, not so much barrel length. Generally speaking the longer the barrel the higher the velocity. The difference in barrel length is 1 1/2 inch but remember that rarely does manufacturer specs match up with the actual velocity, too the outside temperature will affect the actual velocity. Unless you are a purist the difference is not worth worrying about. Also, the 223/5.56 is a very flat shooting cartridge, depending on the load and I am assuming a standard 55 grain load. With the right zero the bullet will never be more than 3 high or 3 low out to over 300 yards. If you hand load it would be a very easy matter to adjust the velocity if you felt the need to do so. Regardless of what ammo you shoot there will be variances in velocity unless you have match grade ammo. You can zero this scope wherever you want with the added benefit that it has range finding ability. By the way, the horizontal line is NOT for windage . . . . . the Chevron is used for that. The horizontal line is in Mil's . . . . . read the manual.