I've done three beers that have all been 100% spelt malt.
SMaSH IPA used 5 lbs Spelt (and 0.5 lbs lactose) on a 2.5 gal batch, 62% mash conversion and 54% brewhouse efficiency, gravity on the day was 1.048
SMaSH IPA used 5 lbs Spelt (and 0.5 lactose, different hop this time) 51% mash conversion and 52% brewhouse efficiency, gravity on the day was 1.048
HefeDinkel if you will, 4 lbs of Spelt and 150 grams Dextrose, 63% mash conversion and 64% brewhouse efficiency, gravity on the day was 1.043.
Also, I recommend milling a little finer than usual. Spelt has big honkin kernels, and my grains the first time around just sunk like concrete in the mash tun. It's so tough and hard like wheat, that I think half of my efficiency issues stemmed from poor crush, but also it could just be low DP on the malt.
Or try step mashing to get some better conversion and efficiency points, but with that being said, Spelt can kick out some serious haze and fluff in a beer when doing a single infusion. If you do a protein rest, it might detract from the malt's profile in my opinion.
Hope this helps.