The "correct" answer is to measure fork length, rake and trail of the stock bike, then fit the new front end and measure to see if it's still OK. In general terms, the newer front end will probably have less fork offset and that decreases wheelbase but increase trail. in all probability it will be fine but it is up to you to make that determination. Old bikes tend to have a lot of fork rake and fork tube offset to get trail down to about 100mm or so. Modern bikes tend to have steeper steering head angles (rake) and need smaller offset (the distance the fork tubes are ahead of the steering stem) to get rake back to acceptable levels.
