That fork is almost certainly not original due to the spacer used under the headset threaded cap. So if it rides "weird", it may not have the right offset. New forks are certainly not hard to come by. Those tires are probably 28s and...if they are, it looks like you could fit at least 35-38s on it...it looks like the chain stay clearance will be the tightest of the three critical areas (seat stay, chain stay, and fork). Those definitely are interesting bikes -- enjoy the ride!