Looking for suggestions and advice...

I'm currently building up a bike on a used steel frame I acquired. The frame requires a 1 1/8" straight steer tube and a 45mm rake. My hope is to convert this bike to a front hydraulic disc brake. There are several forks on the market for Cross bike frames, but they have a longer axel to crown length than this road bike's original fork had. (Forks with straight steerers and disc brake mounts that Ive seen have about 395mm axel to crown length... considerably longer than the stock fork which is approx 370mm axel to crown)

How much would the geometry of a frame (and likewise the way it handled)be altered if I were to install a fork that had approx 2.5cm longer axel to crown length? I suspect it would be considerable.

Secondly, since I don't really want to install a longer fork, does anyone know of a fork on the market that fits all of these requirements but that is not as long as the cross bike forks?

Sorry for the long and possibly confusing question. Hoping to hear some good news!

Stephen