The manufacturers of these bars used to be the australian agent for Caltracs and these appear to be very similar. To use these bars correctly you must have the correct spring rate and correct shock absorber for them to operate as designed. Visit Caltracs website and look at some of the pics of cars using them in the states, small slicks and huge launches!
the specs on that site do not work correctly, even when modified to match our cars, several of us have tried them in the past and although the idle appeared ok with no test equipment, testing them would find the changes you mentioned.
if you are referring to the bolts in the turbo exhaust cover, they have a habit of cracking the cover where the bolt holes are drilled, if cracked there is not enough tension to keep the bolts tight for any length of time and they will come out
The Abvance 4" dump appears to work quite well and if the seller has it at a good price, that's an added bonus. but just a warning to what can happen when going to unknown brands based on what a seller may tell you read about 1 of my customers problems
I'll assume you mean the cross over and then yes it is common for them to break or be broken, they are available from ford for maybe $10-15 each and if you have an end missing you will need the nut as well. Good luck trying to explain to the parts person what you want, It took me a five calls the first time we ordered some.
A good exhaust can help exhaust valve springs, if you have back pressure building up in the exhaust and the manifold, that pressure will be pushing against the back off the exhaust valve which is affectively dropping the seat pressure by the same amount as the back pressure.
different suppliers may have different part numbers, but the walbro numbers are gss 340, gss341 and gss342, all pumps are the same just with different inlets and have the same flow rate.