Why do you think wrong length spindle ? assume you mean axle ? as these are centrered you need to see how much clearance there is between the inner crank ring & the drive side chain stay, its not very clear in the photo, this gap should be about 5.mm, if its over 10.mm could be axle too long, as mentioned above replace all the bearings, cups, maybe the axle if it shows signs of wear, & new cotter pins. At least that way it stays original, if you go for a sealed BB assembly I don't think they are made for cotter pins, so that means changing the whole crank out, very unwise in my opinion.