What do you want to do with the engine? For street use you can use the A15 valve sizes & still have very good performance, but puting a full race head on a street 1200 will give you a really good top end, & if you normally drive at 6,000 rpm in urban areas, then you will really love the difference.

If, however, you only occasionally see the stock redline of 6,500 rpm, then perhaps the mods can be kept in the more 'affordable' range. My own GX head is fitted with 37mm inlets from the A15 [lightened & polished] along with some stainless exhaust valves at 32mm dia. Ports are basicly stock & this will provide all the performance I want, particularly in the all important mid range, which is where my engines spend the bulk of their life.