As a recent and new Cobra enthusiast (and a small business owner), here's my take. I think the Engine Factory sells a lot of 351W, 400 HP motors so I think there's a market for it. You have the option of competing on price and/or options. I bought mine from Engine Factory because it was bolt on and turn on. I didn't need to add anything. But what I don't like is that they have limited options and were not totally familiar with my kit, a Lonestar. As a result, I had to buy a different filter assembly and I replaced the valve covers to match. Offer up some bling option packages for a reliable, consistent 351W assembly and I think you can compete for business.
The sweet spot is to make it easy for non-motorheads to get a reliable engine with the appearance package they want and know it will fit and be complete. Motorheads are going to do their own thing anyway. I differ in opinion with some on the list that everyone wants HP and can build a motor from a pile of iron. I doubt that. Most are weekend tinkerers who would rather drive something that will work and not leak
oil than spend their winters (and usually their summers) fixing and rebuilding.
Just my $.02.