I'm not an advanced expert on these gas piston dealies, but the dimensions of a CARbine (car/m4/LtWt) are different than a (true) MidLength (ML is not a "Dissapator" or whatever).
The gas tube length and thus the gas port are drilled 2" further out on the MidLength (ML).
The handguard on the ML is also 2" longer. (7" CAR, 9" ML, 11" Rifle. These measurements are close enough for descriptive purposes)
You can't really "convert" a CAR into an ML because of the location of the gas port on the CAR. You run into handguard (HG) fit issues when you try to put a ML HG on a CAR Barrel because the gas block or Front Site Base FSB gets in the way. The "Disappator" is an
imagineered cosmetic contraption that looks kind of like a ML.
There are "phantom" Gas Blocks that are very slim profile that may be installed (and even hidden
under certain types of longer handguards).
You can remove and replace a
standard gas block (GB), but if you have a "post ban"
permanently attached flash suppressor, you can't slide it
over and off the muzzle. If you have one of these designs (California?) you can destructively remove the GB and replace it with a two piece "clamshell" gas block. As long as you have .750" maximuym diameter, the regular ones will slide off and on. Pinning them back is the magic trick, the A2 FSB is usually sold as a "take off" when removed, not replaced.
The only advantage to using Mid Length tubes and gear on the CAR length set up is exactly what the above referenced M4carbine.net post was going on about. You can manipulate the function of the weapon by increasing the length of the Gas Tube, usually this is done with a "pig tail" or a coil of tubing (instead of a
straight Gas Tube) that encircles the barrel, looking much like a CFL bulb.
Gas systems have real world applications in improving combat reliability of m16's. A well maintained properly constructed standard AR will perform perfectly for any LE or civilian use.
Here's the Ferrari version:
http://www.lewismachine.net/store.php?cid=11&session=6fe491f1c6ce875e854bbd6c3b4e16f3