That's about all that I did that was different from the PDF. Some random thoughts about the process are below:
I wasn't able to use the angle grinder flapper to shape the seat. When I tried the flapper grabbed the foam and pulled the grinder out of one of my hands and it hit my other hand and took out a few chunks. I end up using a belt sander instead, so be careful with this step. I also added two strips of foam to the back of the seat, to create a valley, so it held my spine off the backing, it made for a more comfortable ride.
I didn't have scrap bikes laying around for parts, I spend more time than I should have sourcing them, and trying to find matching head tubes was nearly impossible. I realized I could have gone to a dept store and bought two bikes for about 200 bucks total and used them for parts. By the time I bought 3 chains, new peddles, a chain guard, new brake pads, handle bar grips ,bottle holder and cleaned all the rust off the derailures, wheel, gears, etc. It would have been more time and cost effective to use new bikes and have new parts. Also when I was done, I had a "new old" bike, some I can find parts for, some I can't because there are so many head tube sizes, and wheel sizes and ISO numbers and even the size of the threads on the peddles can vary.
Try not to commit to welds as long as possible. I had tons of clamps and wood jigs holding everything and it made it very easy to see issues ahead of time and correct without having to grind, weld and tack a million times. I went to harbor freight and picked up a clamp or two every visit, they're resuable and cheaper than screwing up steel and another trip to the supply house.
A tip from the bike shop in town, for setting up the gears. Since a normal bike stand won't work for trikes, he said for trikes, striders, quads, he uses jack stands. I took his advice and it made it so much easier to get the gears tuned up and they were very stable and I wasn't concerned with the weight of the trike.
Think about a rear fender if you ever ride over any water or anything you don't want flung all over the back of your head.
I used a mig welder and it used about 2lbs of weld through the whole process.
Snow works really well to cool off hot steel parts.
Menards had spacers for the axels, but lowes had better ones. Menards also had the tube/cable guides, and the spherical rod arms, but they were half price online at automotive shops.
I couldn't source v pulleys, so i ordered from amazon the kind used for cable weight machines.
I didn't do anything expensive for any of this. I used a harbor freight vulcan welder and 100% CO2 (I had co2 for airbrushing but not the argon mix) all my tools are ryobi or generics. When I could buy any consumables a harbor freight, I did.
All in all, the cost by the time I was done, if I included tools I bought to make it (chop saw, welder, welding PPE, etc) it was probably about the 1600.00 USD. The most expensive "bike part" was by far getting the front wheels laced up at a bike shop, but well worth it as it saved me a ton of time and frustration I'm sure. Not counting the cost of the tools, (because really i'll use them on other projects and it was an awesome excuse to buy more tools) this was far cheaper than buying a "real" trike. I also figured after I make one, I'll have others in my family that I ride with, want one as well and that will divide up cost of the tools over each bike making them all cheaper and cheaper to make. I'm glad I went this route instead of buying one and the only difference between the two that I don't like about it, is it's about 51lbs, which is heavier than the store bought, but not a deal breaker or anything that makes it unusable.