As a professional fabricator/machinist, I bought a td conversions adapter kit instead of making my own. For me, it's more efficient to buy an adapter and spend the time saved doing wiring, tubing work, other misc fab/machining. That's an easy 30 hours of time I can put towards tasks that got the truck on the road faster.
By the time you pay a local shop to measure both engine and trans, design the plate, design the crank adapter, and make a starter work, you're not going to save any worthwhile money (and especially not time). There's a reason adapters are expensive; there's A LOT that goes into them to work well and not kill pilot bearings, clutch disks, or trans input bearings. Following the rules of business, the more products you make, the lower the profit margin needs to be. So the local machine shop making 1 adapter needs to make a good profit on one kit in order to keep their doors open. TD Conversions or anyone else only needs to make say $100 on each kit because they sell 5 a day.
Now if you were to design your own and just have a shop cut it, that's another matter. But if you had the skills to design your own adapter, I'm willing to say this thread wouldn't have been posted. I'm not trying to come off harsh or anything, but being in this business for over 10 years that's my experience. We all like to save money, but sometimes the pennies saved now end up costing many dollars later.