I'm 6' 4 1/2" and pants are 34x34. (I was 36x34 the last few years and started pushed my way up to 38x34, but I said enough is enough and 6 weeks of effort got me back down to my college size of 34). So anyway, the only real difference between me and your brother in law is the leg length. His extra 2 inches of leg length could require a little extra deck height (from some extra freeboard). But we should be in the same ballpark. The only other thing to worry about is shoe size. Since longer legs put feet deeper into the boat, it can get too narrow to fit yout feet. I have size 13 feet so see what he has.
I paddle a P&H Orion. It is not listed on their website, but you can still custom order them. Awesome boat. It is fiberglass and I think it weighs like 47 or 49 lbs. Highly recommend the P&H boats.
If he gets a plastic boat that fits him, it will be heavy as a tank. My first boat was a Wilderness Systems Sealoution II XL. The XL was the big and tall version. They dont make it anymore. It is a battleship. It's like 60 lbs. Good for multiday trips because you can load everything but the kitchen sink. It is a lot to handle on a day trip though. I still have it, might sell it to him...
Is there a reason he wants plastic? If it is just cost, then I highly, highly recommend he buy a used boat (I recommend that for everyone buying a first boat). He can get a much better used glass boat for the same price of a new plastic boat.
But anyway, you mentioned the P&H Scorpio. My friends Sam and Carl at Osprey Sea Kayak Adventures have a used one for $1400:
http://www.ospreyseakayak.com/index.php?section=55
I've never paddled one, but maybe I could check it out for you. (just checked the P&H website - it is 63 lbs! yikes! you either have to be the governator or always paddle with a buddy)
But then they also have a nice Valley Argonaut kevlar boat for only $1800. That is supposed to be ok for larger paddlers but I haven't tried one. Certainly worth giving them a call or swinging by. Let me know if you do, I'm like 5 minutes from the shop.
- darren
ps: the Current Designs Gulfstream is essentially the same boat as my P&H Orion. They are a production boat and can be found in numbers on the second hand market (there are literally only a handful P&H Orions in the US).
pps: just saw that my friend Dave is selling his (very) used Gulfstream:
http://www.nspn.org/forum/index.php?showtopic=6913
Doing some research on it. P&H says it wont absorb water in case of puncture. 
