Really? I've seen a few people ride with toe clips that they don't always use, leaving the clips on the lower side of the pedal. They don't drag on the ground and certainly don't interfere with cornering. If you're wanting to do this to a fixie (you didn't say in the OP) and cornering is a problem then if your primary concern is about the looks put something smaller on.

That would work.

Back when I rode with toe clips and straps, leaving them on the underside of the pedals would always have them scraping along the ground until I flipped the pedal over. And, these were medium-size clips and size 9/43 shoes on a standard road bike with a normal height bottom bracket and 170 mm crank arms so nothing particularly oversize anywhere.

Why not make a type of platform where there is an SPD cleat attached and can be fitted with clips and straps which just clips in to the pedal. Just twist if off when using your SPD shoes. Or as an example you could just buy these or find something similar. Amazon.com: Exustar SPD Clipless Pedal Adapter: Sports & Outdoors It won't give you the proper "vintage look" but trying to fark around with clipless shoes/pedals with clips mounted may change you mind very quickly. You could also mount a quick release pedal axle system that would make changing pedals fast and easy. http://www.bing.com/images/search?q=...xles&FORM=IGRE

The M324 has reflector mounting holes so you could probably bolt on the toe clips. The straps are harder because there is no mounting point on the inside of the pedal and routing the strap may interfere with the SPD side.

The VP X93 pedal looks like it has the inside strap mounting point but that's probably because they're reusing an existing platform (and it only comes in black).