morbias

Keep in mind the jacking point strengthening panels are inside the dog legs and could need replacing if they are rotted. As far as I know, repros aren't available so they would have to be fabricated.

This. I swapped my dash bulbs for leds, pretty sure a couple of the sockets were wired the 'wrong' way around for leds. I ended up pulling the ends off the leds and soldering them back on reversed rather than rewiring the sockets.

A bit further up the page you mentioned you don't know what engine setup you have or what sort of needles you have installed; that's pretty critical with regard to your issue tbh. You really need to hook up a wideband O2 sensor and AFR gauge to figure out what's going on, or even just take the car to a shop and see if they'll hook up the gear they use for the emissions test while you rev the engine. That would at least give you some rudimentary idea of if the carbs are leaning out further up the rev range - if they are then no amount of fiddling with the carbs is going to fix it and you probably need different needles, assuming the carbs are in good working condition and don't have hidden issues like worn throttle shafts.

Without reading the whole thread again, I would suggest checking the ignition system including strength of the spark, whether you have the correct weights and springs in the distributor, whether the variable timing plate in the top of the distributor is moving freely, if the vacuum advance is functioning properly. It also might be worth checking your valve clearances if you haven't already.

I agree with what you're saying re the drip rail, but there is an added potential for a bolt to break the surface layer of the stainless and the paint layer on the mild steel so it acts as a conductor. Also, the potential for battery acid to get between the layers greatly increases the probability of a conductive environment forming.

I personally wouldn't even risk bolting it in to be honest, stainless steel contacting mild steel will result in the mild steel rusting at a faster rate than normal.

They look like Momo Altairs, no idea what they're worth though.

Are your door bumpers missing? They should be fitted to the lower rear corners of the door openings, if they're missing then that could possibly cause this issue, though I would have expected the door rubbers to be enough to stop the doors moving when closed. Are they the correct weatherstrips because new weatherstrips usually cause the opposite problem where the doors are hard to close!

Is it backfiring through both carbs or just one? Backfiring through the carbs can be caused by a lean running condition, if you have a white plug then it would suggest you are running lean on that particular cylinder for some reason. Perhaps the manifold gasket isn't sealing properly and is letting excess air in to that cylinder?

Have you put new fuel in it? Carbs don't like old fuel so much.

Might be worth checking the back of the fuse box itself to see if there is a problem there.

Worn hinge pins perhaps?

The floor is supposed to move the driver/passenger away from a side impact, so I would have done full welds on the sides and spot welds along the front and rear to best mirror the original design. Agree with above though, that welding job does not look the best - also, the beads holding the frame rails on seem to be few and far between.

The factory mustache bar is supposed to have that twist in it. Are you sure you have the correct T3 bar because they make 2 'stock' versions, one for the r180 and one for the r200? Also, have you tried bolting the original diff in with the T3 mustache bar, that will tell you right there if the bar is the problem.

The amount of droop is determined by the length of the shocks at full extension and if you are using roll center adjusters that will also increase the angle of the anti-roll bar towards the sump. Also, using stock strut mount insulators instead of aftermarket top mounts with spherical bearings will also position the control arm lower.