Welcome to THR!
Is it possible to install these on a newer model, say an 870 express?
Is this something that I can do myself or would I need a gunsmith?
It works well, I have 'take-off' Police gun furniture on a couple of Expresses here, and I like it.
Stocks are generally not a problem to change out- it takes a #2 Phillips to get the recoil pad off and a long-shank slot screwdriver to remove and replace the buttstock. Keep in mind that some synthetic stocks don't need the stock bearing plate that wooden stocks do- be sure you have the right amount of space in the back of the receiver for the 'socket' of your stock to fit into. You may have to put in a bearing plate if your gun doesn't have one. Chances are a bearing plate won't be included with a take-off stock set. (See
http://www.urban-armory.com/diagrams/rem870.htm , it's Part #60)
Actually it's pretty easy to swap out fore-ends a lot of the time, but when it isn't easy... well, you can mess stuff up trying. Best bet is to buy a good fore-end tool if you plan on doing lots of mods to 870s in the future. For a one-time thing I'd get someone who had the tool and some experience to do it. It can be a bit tricky to get the new forearm lined up so it doesn't rub on the barrel sometimes too- that's easier done by someone who has some experience.
I was looking at the 870 Express Synthetic 7-Round:
http://www.remington.com/products/fi...ound_specs.asp
This raises one more question: Can this model also be fitted with a 26" or 28" vent rib barrel if I decide on getting one in addition to the 18"?
That's a good choice for a platform to start building the gun you want IMHO, if you want to start with a HD type gun. You get a good magazine extension off the bat, plus you don't have to mess with magazine tube dimples.
You CAN put on a longer barrel. You'll need a standard magazine cap and a standard length magazine spring. I'd find one of the old style spring steel magazine spring retainers just to make life easier while the gun is in sporting configuration- and don't forget the plug, if you go after migratory birds.
If I were you I'd look for an older style Express barrel (or a Wingmaster or Special Purpose barrel- you can use anything in the same gauge but a Special Field barrel) that has the detent in the barrel ring (to keep the magazine cap in place), and get one of the old style magazine caps that has dimples around the outside edge to engage the detent in the barrel ring. Newer Express barrels don't have the detent, the newest ones don't even have the hole drilled for it. Without the detent you will have to jackleg some way to keep the magazine cap tight, like teflon tape on the magazine threads or something. It might take more looking to get the parts to do it 'the right way' but would make life easier in the long run.
Have fun, stay safe-
lpl/nc