There is something of an axe to grind from Paul Roddison in that thread, slight pinch of salt required to some of the comments from him I feel given the massive fall out he has had with BBR over various matters (yes BBR would not pay Paul Roddison to conduct warranty work to fix cars with the BBR turbo kit for people who had problems, but this is purely because of his previous poor workmanship on cars he'd fitted kits to, which BBR later had to rectify themselves...this is not explained properly in the thread).
Having used both tuners (Roddisons and BBR) and spent 4 figure sums with each I know my car would not be going to Roddisons again and I am not the only one who feels that way, BBR I would go back to happily though.
That thread is about the mk3 turbo kit that BBR developed themselves too, the mk1 turbo kit they sell now is a rebranded BEGI kit I believe, sourced from the US, so totally different really.
If I was after a 300bhp mk1 engine build for track work I'd also be speaking to Ardler Automotive (a very nice looking and newly engineered turbo kit available through these, manifold is a work of art and above the usual log manifold design used on these) and also AK Automotive who built and race a very high powered mk1 turbo (390 odd bhp).
Reliability is tricky at these power levels on track, gearbox as much as the engine itself mind. With used 6 speed gearboxes being so cheap most seem content to just replace the gearbox several times over a track or race season, rather than the hugely expensive options of a properly engineered gear set (the quiafe one is crap and gives better ratios for racing but is no stronger than standard) or a gearbox conversion to something stronger.