I think the '88's had either the poly or metal. If it's a 15 gallon, it's most likely a metal. If it's a 20 it's a poly. I've heard of either tanks being in the earlier years.
As for the transmission, it seems like it might be low on oil, or the clutches are giving out. Auto transmissions are tricky for me.
Now, I could be wrong but I think for the AX-15's they have a line from the main cylinder (behind the pedal) to the transmission. You could either try to get the LHD line to work, or custom make your own (or even buy the LHD line, if you can find it).
I think everything else is the same. Check a transmission diagram to make sure. [Also, don't settle for the BA-10 or whatever number that came stock in the 4.2L, they are terribly unreliable and weak. Also I believe it has the same bellhousing pattern as the AX-15, so it's a direct swap.]
And dependent on your state [whether or not they have emission tests] you can buy a carter / replacement Carb, and do what they call a 'Nutter Bypass' to remove a lot of the vacuum lines. If you can get it for 1250 [most likely can], you put another 2k into it [Carb+transmission+tune-up], you'll have yourself a running heep.
You obviously don't have to get that one, but it looks like there's some ability to move it around and path it how you want. So, it's doable with LHD stuff.