Just found someone on here who's done the conversion with a 998 plus a few things like forged pistons and rods and a weber, reckons he can get 180bhp with a 1275 block. I'll get questioning!
180 out of an NA 1275 is going to take some doing
But is still realistically achievable with the BMW head. I've built a 164bhp 1330 which was still nicer to drive than an equivalent 5 port head engine with a 286-esque cam. KAD have done over 200bhp with there kits and have proved very reliable in a competition engine sense.
To the OP, that kit on ebay isn't actually a bad price for the head and related ancillaries. However, as people have said it is far below the price of a completed engine. Bottom end wise, unless your sticking with the 8 valve, these engines like to rev. Because of that modifications i recommend at minimum a center main strap to be fitted, whilst often pushing towards the 4 bolt center cap and steel end cap set. Its then machine work to get these fitted plus a rebore to whatever you fancy/require. New pistons are obviously needed, and they have to have the 16v cutouts in them, cast Omegas are really good. Up to about 130bhp you should be okay with standard rods, anything above this you need to look into H beams. The whole bottom end needs to then be balanced including the flywheel. The head then needs several passage ways/pushrod holes blocking off, with additional holes drilled for the new BMW head. The head itself then needs a fair amount of machine work, with the timing face being machine off to sit flush with the block, also pulleys are now used instead of sprockets. Once you get to that point there's still a fair amount of work involved in the cooling and oil supply system. As well as setting up TBs and then relevant mapping to suit.
The bit above may sound a bit scary, thats not my intention, unfortunately due to dodgy eBay adds like the one you posted, people buy these kits expecting there head to just drop on and they can be away with double there original power. It doesn't quite work like that. Don't let that put you off though, if your willing to make the investment, the performance produced by these is completely different to that of a 5 port a-series. Unless your going for big cams, the torque curve is awesomely flat, and the power buids completely linearly, making a lovely engine that is easy to drive in traffic and around town as much as it is willing to fly around a track.
