cant choose enclosure type

Are you going for spl or loud and good sounding? 

The subs in a ported box tuned in the low 30's should yield a good overall sound that is loud.    You can tune the ported box in the 40's or even 50's to create a higher spl, but it will sound like garbage.

The ported box tuned in the low 30's will probably still be louder than the sealed box at 43.  The way I understand it the sealed box is not really tuned to 43hz, thats just the resonant frequency of the enclosure.  This will be where the enclosure peaks, but should not be significantly louder than any other frequencies.  On the ported box you will theoretically pick up 3dbs at the tuned frequency.   If the ported box is designed properly, you should be able to get something that sounds just as good as a sealed box but a little louder. 

if you are competing or going strictly for spl do a big ported box with a high tuning.  Model it up on some box building programs and see which tuning frequency gives you the best peaks.  Keep in mind the enclosure will not sound that great when listening to music, and the box has almost no control over the sub below the tuning frequency.  This means if you are playing music with bass below the tuning freq, you run the risk of destroying the suspension in your sub.

If you want a good balance of sq and spl, a large ported box in the 35hz range should be the way to go.  Too much lower your gonna sacrifice output.  Too much higher, your gonna have horrible response. 

135dbs on a term lab is pretty good for 2 type r's in a daily driver.  Those subs were hardly designed to break any world records for spl. 

You may gain a couple of db's by repositioning the subs but probably not worth the effort.  Most likely be inaudible anyway. 

If you want to get up in the 140's and still have some type of sq, I'd probably reccomend different subs.

double the power, you should see a 3db gain.  Maybe a lil more with cabin gain.   You will have a severely underpowered electrical system though.  You'll def need a high output alt and a very good batt, two batts wouldn't hurt.

If you play with it enough you will get into the 140's.  Don't know how much your gettin those amps for, but new subs on the amp you already have might get you where you wanna be a lot faster. 

I have not had a whole lot of exp working with the type r's but I think they were geared a little more on the sq side rather than spl.  A sub designed for spl in an enclosure designed for daily use might get you where you want.  Possibly one good sub would be enough.  I know Jeff is gettin in the 140's and even 150's with relatively musical set ups on single subs, under 1000w.

What car?  Some cars are bass traps and a little more challegning than others.  If the box is blocking the bass, then try facing the subs forward or up.  You might consider a bandpass box that vents directly into the cabin.