Record's combination/plough planes went a bit metric toward the end...... say, early '70s....... though they never went the whole hog. Besides, in many projects made of wood, ploughed grooves are rarely dependent on precision. If they are, then best solution is to cut them narrow and to adjust the sides to the exact size you need with a side rebate plane.
Now, as a general rule, all the plough/combination type planes by all the manufacturers over the years used blades of varying widths and configurations, but they all had one thing in common - they were 1/8 inch thick and relied for their fixing in place on either a compression grip under a screw (Stanley 46 etc,) or a grip between two grooves, (Stanley 50 etc,) with the adjustment, fore and aft, usually being a screw/slot/groove arrangement engaged in the end of the blade. Each maker had a different adjustment and their blades all looked different at the top end ...... except that they are all 1/8 inch thick.
What this means in practicality is that, if you disregard (and temporarily disengage) whatever adjustemment mechanism is on your plane and rely on adjustments by hand, almost all the available blades by any maker, old or new, are interchangeable, if they are 1/8 inch thick.
One other thing that distinguishes "modern" replacement blades is that many of them that I've seen in the UK are rectangular in cross-section.
If you look closely at older, original blades and measure them with a square, you'll see that they are actually trapezoidal in shape - in other words, the cross section is wedge-shaped - the edges taper by a degree or two from the front (flat) side to the rear (beveled) side. This allows any play in the two two skates to clear the sides of the grooves as it gets deeper. Rectangular blades tend to get wedged in and offer more friction to the work.....
Hope that this helps, good luck with it - don't get too bogged down in precision!
