This was a bold attempt by Swiftboost. By the end of the thread (May '11 to Feb '13, the final post by Swiftboost) the project was still at the tinkering & developmental stage! I saw no mention of any combustion space parameters (Peak pr./compr. pr / and most importantly, the MEP (mean effective pr) being recorded. The peak pr. value determines the stress threshold calculations for the engine scantlings. The MEP value gives a broad guide-line for the torque (& thus the power) output.
Aftermarket turbo kits were popular in the UK (& elsewhere) way back in the 70's too, with firms like Broadspeed Bullit offering strap-on turbo-kits for the Vauxhall Firenza & Ford Escort among others. These were popular among week-end boy racers and they had the usual draw-backs - they ran quite well for a while and then started to gradually fall apart!
So for folks who have the time & the inclination (not to mention the deeper pockets!), this would be a great hobby. But for anyone hoping to do this kind of home up-grade in the belief that the end result would be a lasting & problem-free experience, I feel would be more optimistic than prudent.