I would say offer him more to get everything as it will most likely cost you more in the long run. Your VTiR gearbox will fit although, i think the gears are way too long. You will have so much more fun with an ITR gearbox with the LSD.

Another idea if he cant provide recipets, is for dyno printout - or the best thing is to witness a dyno run (if it is still in car) to get ana ccurate indication of power which will give you an idea if he is talking sh!t about the mods or not.