most steel frames of that era were a bit loose for ease of fitting the wheel. Nominally it is probably 126mm, with an extra mm or two on each side. You could fit a 130mm OLD hub in there quite easily.
The freewheel has nothing to do with the OLD of the hub.
A couple places on the 'net mentioned a 27 x 1¼ wheel and tire for the Peugeot Marsielle..... Do the brake pads line up nicely with the brake surfaces on the rim?
Nigel
130mm free hub is feasible. You'll need a cassette. Go with an 8/9/10 speed freehub and an 8 speed cassette. You will need an 8 speed chain.
Nigel
8, 9 and 10 speed cassettes are all the same overall width, any freehub that will fit one of the three without a spacer will fit all of the three.
Before you purchase new wheels:
* figure out what you have (OLD of the hubs, BSD of the rims, width of the rims and tire size; tire size in ISO measurements for example 37-590).
* measure how they braking surfaces are lining up with your current brakes
* measure how much clearance there is between the frame (and fork) and the current tires on the current wheels properly inflated.
It would be good if you did not spend money on something that will not fit your frame.
Jeff: 26 x 1 3/8 is either 590 or 597 - the later is Schwinn.
An early rigid frame (no suspension) mountain bike (MTB) can be made into a great road machine with just a change of tires and tube. For example a early Specialized Hard Rock; changing the tires to some high pressure (100psi) Kenda K193 Kwest 26 x 1.5 tires and suitable tubes.
Avoid suspension
Nigel
clearance, measure the gaps.
BSD is bead seat diameter - 590mm in your case.
too fit a 32-622 (700c x 32) wheel and tires, you will need more than (622-590)/2 - (37-32) = 11mm clearance between you current tire and the brake bridge and bottom of the fork - at that point the 32-622 tire will be rubbing; and you will need to adjust your brake pads (622-590)/2 = 16mm higher than they are now.
Nigel
In the case, distance from the tire to the fork at the crown - how much radial clearance is there for a larger diameter tire?
Right now, you are looking a $200- to $300- min to change to ISO622 (aka 700c).
Nigel
Yeah, OK, I'm lost! Why wont a 700c rear work with those brakes? The pads are high on the 590 brake track as it is, so they would have to come up less than 16mm to hit a 622 brake track.
You buy one 700C rear wheel, 130mm OLD, listed as more than 7, less than 11 speed. 32 spoke would be OK as the rider weighs less than a German Shepherd. I still think 36 would be better if you're gonna get a little abusive though.
You leave the front alone, to save money, if you can handle the white wall look. This gives you years of use out of the front wheel as you now have a spare tire & tube.
You purchase a chain, a cassette and use , borrow or buy a chain tool, a cassette tool & a chain whip. Once the rim comes in you mount it, look at it, & decide what tube & tire you want to buy for it.
Or like nfmisso says, $200 + for 2 wheels/tubes/tires, on top of the cassette & chain money.
I was able to acquire a set of used 700c wheels. The rear wheel fits well along with the brakes.
Unfortunately the front wheel's axle diameter/width is slightly larger than my fork ends (about a mm or less).
What is the standard axle diameter/width of modern front wheels?
9 or 10 mm or more/less?
Can I file off a mm of my fork ends to fit the wheel or should I just find a new front wheel?
standard today on front is 9mm for road bikes and most hybrids.
other standards include 10mm, 3/8", 14mm.
filing - maybe - if there is lots of metal there.
Nigel
If you do the axle, make sure that the flats match on both sides.
This is easiest to do if you take the axle out of the wheel; note where the cones are, take the cones and lock nuts off; then run a two pair of axle nuts in all the way and jammed together - one pair on each side, so that you can chase the threads after you are done, and use the nuts to hold the axle in your vice and keep the axle's orientation while you do the filing/grinding.
Nigel
If you do the axle, make sure that the flats match on both sides.
This is easiest to do if you take the axle out of the wheel; note where the cones are, take the cones and lock nuts off; then run a two pair of axle nuts in all the way and jammed together - one pair on each side, so that you can chase the threads after you are done, and use the nuts to hold the axle in your vice and keep the axle's orientation while you do the filing/grinding.
Nigel
You can use the side of the vice jaw as a guide to run the file against for accuracy, or you can even slide a washer, or a spare nut on the axle, to use as a guide while you file. You end up with a clean looking job.