Hi,
Agree with the difference in barrels and using part numbers but some manufacturers don't appear use such things!
The two well known companies I've used both have an actual bike rigged up to fit their pipes to - though the first (and totally un-helpful and rip off) company I used must have had their lugs in different places to mine - had no chance of fitting despite the size of hammer.
If I was to replace the pipes again I'd try and buy the pipes unchromed and brackets seperate - then get them to fit properly, weld up and then re-chrome but.... that's next time as if.
RR