Shafting / props

Wouldn't you know this subject comes up next - I'll take two. Throw in some new couplings, too. Here's my deal: The motors are just sitting on the stringers, maybe a couple of bolts in place just to get it here. I have the old shafting and that's what I was going to use to do the preliminary alignment. In the water's got to be the only way to get it right. I think the old shafts are about 3 inches too short. I had considered getting some 1 3/8 stock and get something at least a couple of inches too long, just in case, line it up, measure it all and get the machine work done. Except - this boat had come with 427's - that's the reason for the big shaft. The 327 boats had 1 1/4". So, I'm going with 350's - 240 hp with almost the same gear ratio (1.54:1) the original was 1.5:1. The boat came with 15 x 17 props, that's fine - I have a new set. The only thing is, the local prop shop tells me that the prop required to fit a 1 3/8" shaft has to be
16 x whatever. The 15 x 17 is probably what I need, my intention when I got the props was to make them fit the shaft. The prop shop tells me that the hub doesn't have enough material, looks like there's a lot of brass there. I guess I could get the 16" if I had to, then get it cut or squeek by with it if it would work. I just hate to have this set here and not be able to use them. Has anybody else gone through this kind of thing? I really wanted to keep the big shafts and I really don't want to machine a 1 3/8 shaft for a 1 1/4 prop. Any ideas?