Triple (mtb) crankset for old road bike SS conversion?

Noobish question. I'm going to convert my 70's road bike to SS. Since it has cottered cranks I've bought another used cotter-less crankset on ebay. Chainrings are bolted by 5 bolts I assumed it's comes from a road bike. I haven't noticed third chainring then (blurry Ebay picture and not enough attention). Now I started to doubt if triple crankset was a good purchase. I know I should have done my research earlier...
It's a Exage 300LX crankset just like the one in picture bellow.

Is such crankset usable for SS conversion?

Not ideal but it should work. The inner chainring uses a different set of bolts and can be removed and discarded. The middle or outer can be used for your SS depending on the gear you want. You'll need to replace the existing chainring bolts with a set of narrower single chainring bolts, and then decide which side of the spider to mount the ring to get the best chain line.

It's an MTB chainset, which typically has a wider q-factor and chainline than a road chainset.
Added to which, your road bike may be old enough to have 126 rear spacing, whereas an MTB has 135.
I think you're in for a headache unless you use an ss/track/road chainset.

I could of course be talking out of my arse and somebody else may show up with some pictures of Rivendell-esque 27"/700c touring frames rocking MTB triples. I doubt any of them will be SS though.

It's an MTB chainset, which typically has a wider q-factor and chainline than a road chainset.
Added to which, your road bike may be old enough to have 126 rear spacing, whereas an MTB has 135.
I think you're in for a headache unless you use an ss/track/road chainset.

Crap... Not that I've spent a lot of money on the crankset just would prefer not to waste any at this point :-|
Haven't measured rear spacing yet but my frame is like this one: Velobase.com

On the bright side. Started to strip the bike this evening. Deraileur, shifters and cottered crankset are gone. Cottered BB came out easier than I expected. But couldn't remove freewheel with household/car tools I have. Hammer and flat screwdriver didn't work ;)

You won't have any problems provided you're happy to do a little fettling.

MTBs (especially older ones like the ones these cranks were designed for) generally have a wider q-factor than road or fixed bikes, so they are designed to run a wide bottom bracket (say 117 or 122mm). Track/SS bikes tend to run a narrower bottom bracket (103 or 107mm) - which is good for chainline when using a track hub - but if you try to install these cranks on a 103mm BB then the inner ring mounting points will foul the chainstay. The good news is that since you don't need the inner ring, you can simply get a hacksaw and cut these protrusions off, allowing you to run a narrower BB. You'll have to experiment to see what size BB you can use - always leave 2-3mm between crank inner and chainstays to allow for flex.

They are actually very good quality cranks (forged construction) and, although a bit plain, are quite handsome.

If you're desperate, you can usually remove freewheels by holding them in a vice, tightening them up so that the bearings are crushed and it cannot spin in either direction, and then rotating the wheel. This will always destroy the freewheel but only occasionally destroy the hub.

Track/SS bikes tend to run a narrower bottom bracket (103 or 107mm) - which is good for chainline when using a track hub - but if you try to install these cranks on a 103mm BB then the inner ring mounting points will foul the chainstay. The good news is that since you don't need the inner ring, you can simply get a hacksaw and cut these protrusions off, allowing you to run a narrower BB.

If you're desperate, you can usually remove freewheels by holding them in a vice, tightening them up so that the bearings are crushed and it cannot spin in either direction, and then rotating the wheel. This will always destroy the freewheel but only occasionally destroy the hub.

I was thinking about 103/107mm BB too. Just have to find out somehow which one works better in this situation without buying both.
As for the freewheel I will probably just take it to LBS to be removed for a small fee. I don't have a garage/workshop to work in and therefore no vice.

Thank you for the tips!

Just in case someone has same question. Finished converting my bike yesterday and had first ride on it.
Had to grind of mounting points of third chainring. Bought a 103mm BB (needed one anyway because of cottered original crankset). Also took rear wheel to LBS for re-dishing. That's it, got near perfect chainline.
Learned the basics about bikes in progress. Totally disassembled the bike myself for sandblasting/powdearcoating and re-assembled it. Everything about bikes seems a lot less daunting now.

Good to hear it went well, pics/build topic?

It's nothing special really. Budget conversion. But I will snap it next time.