Few things to note. My engine is actually NE90 not SP90 so Atlantic Diesel did not marinize mine.
There was no marking on my pump gear. I ended up getting to TDC, then a mark on the engine crankshaft gear was facing the pump gear. Unfortunately, there was no marking on pump gear. No marking on pump gear anywhere whatsoever along the entire perimeter. I placed a mark using a centerpunch. Injection Pump gear is keyed so there is only one way to come in on the pump. I took off the gear and drive hub and shipped the pump for service. Injection pump service guy walked through the marks with me and I think I should be good.
As far as that tool, I think its fine if it takes me few tries to line up my mark with engine's crankshaft gear mark. We wont know until i put everything back together.
One interesting note is that drive hub (item 2 in pic attached) mounts to IP shaft using the center nut. Ring Gear(item 1) mounts onto drive hub via 4 Retaining screws(hex item 3 in pic). Gear actually has slots where screws go through which allows for fine-tuning. Then retaining plate (item 4) keeps gear from moving along slots. I guess fine tuning cannot be done while engine is idling. This is different from rotary type Injection pump like Lucas CAV DPA that sits on perkins and westerbeake 4-108. That pump you can rotate while engine is idling to fine tune the timing.