It’ll reduce the trail slightly and make it a little quicker on the steering front, but you’d get used to it quickly and it’s a fairly small change, you *might* not even notice.
What fork is on there at the moment? If it’s a boinger then any rigid is likely to feel livelier anyway.
TBH, I’d hold out for finding a P2, they pop up quite regularly in 420mm A2C which will be fine on that frame. Are you going to stick with rim brakes or after disc?
The disc P2s are often a fair bit heavier and not as comfy as the lower legs are beefed up (as is any disc fork), the mid-90’s triple butted rim brake only ones are the best of the bunch. can ften be had 2nd hand for £20-£40 on here and RetroBike forum.
Another option is a 425mm A2C Salso Cromoto, which in my opinion is a nicer ride than the P2s anwyay, but also a bit hard to find in stock anywhere!