SR15's are awesome rifles, but unless you're left-handed they're kinda overkill. Have you seen the special on Smartgunner.com for DD uppers? If you're looking to blow a bunch of cash buy one of those uppers, get a good lower, and give me the extra. I really want one of those DSA Imbel FAL's that AIM has and after stocking up on 2500 rounds of .308 I'm short on the cash for the actual rifle, so help a brother out.
In all seriousness, it sounds like you're looking to spend more than you need to. SR15's and MRP's are excellent weapons but are overkill. Esp pistons. If you're going to SBR than why don't you just buy the lower now and start the paperwork... kinda pointless to buy a 16" upper now just to pay to cut it down in a few months.
Patience dude... patience...

