If you chop the barrel, I suggest chopping it to a length for which suitable iron sights are available.  The Para sights were intended for a Para-length barrel, and are less than adequate for a full-length barrel.  IIRC, the Para sight is pretty crude in comparison to the FAL rifle sights, which are also relatively crude compared to the excellent rear sights on the M1/M1A.  In fairness, very few rifle iron sights come up to this level.

YMMV,  but I will NOT have a rifle that does not have useful iron sights.  In the  case of full-barreled FALs. the battle-sight zero is 250M.  This means at zero to 250 M, just point and shoot.  I don't know at what distance the Para sights are zeroed for a BSZ, but it certainly is less than 250M.  .    

Maybe not chop the barrel, and remove old one and install Para barrel.  Then sell old barrel, as long as it's a decent one.

I retrofitted some 700M sights to my much-modified DSA StG 58A, and while not yet shot at 700M, the printing on the 200M target tells me they are GTG at 700M.  It's nice to be able to reach out and touch someone, particularly at ranges where they cannot usually be expected to reply.

While it is possible to sight-in any optic to a given range, if the optic has reticular hold overs for your cartridge, they will become increasingly low as the range increases if your barrel does not allow the bullet to develop the velocity for which the optic (and thus its' reticular range marks) was intended.  So forget buying an ACOG for your Para, and having work out to its' full range.

I concur in the weight-saving advantages of an aluminum lower.  Done right, as DSA has done, they won't wear out.  The weight savings are enough to offset the addition of a quality optic and rings.

The aluminum mags are also very worthwhile.  I have a number of them, all with new springs and painted with Brownell's AlumaHyde II.  Hard to get nowadays at reasonable prices.  I think I paid $5 each for a ten-pack of new Al mags from DSA long ago.  Steel mags at that time were about $2, IIRC.   I never use them,  I have plenty of refurbed steel mags.

One of the more worthwhile mods I made to my FAL was a Falcon Arms Trigger Pull Reduction kit:http://www.falconarms.com/fn-fal/fn-fal-metric/fn-fal-metric-trigger-pull-reduction-kit-new.html..  This is all you need to finally get a decent trigger on your FAL, as long as the rest of your trigger group components are GTG.  They have all sorts of kits based around the magic springs.  If you have very good HTS components, as I did with the DSA StG58A, the simple kit is all you need. This kit transforms the usually crappy/heavy FAL trigger into something quite decent.  I strongly recommend it.  If your HTS components are junk, as are found in a lot of FALs, then go for  a more expansive kit.

My PARA is far heavier than my L1A1. it's a Brazilian steel lower assembly from Sarco years back. other than that it's my favorite rifle!
I'd like to find a lighter PARA stock assembly.....