Cool project! You've already gotten some great advice. Here's some more stuff to consider as you continue your build:
1. Riffle Height: Not sure about the Proline 2", but Keene's dredge riffles are 7/8" in height and the riffle set you use when you convert the dredge into a high banker uses riffles that are 1/2" in height.
2. Riffle Spacing: 2.375" is way to close together. Putting them that close drastically compacts the vortex in between the riffles and makes it practically useless for sorting, retention and discharge. Sanman and I experimented with riffle spacing by creating multiple sets of riffles with various spacing and angles. We tried 2.5", 3", and 4" riffle spacing and ran each set in a washplant sluice for a full day. The 2.5" riffles did not work well at all. 3" riffle spacing worked really good but required a steeper angle and more water. The 4" riffle spacing worked the best using normal angle and volume. Of note, the Keene 2" riffles are spaced 4" apart in both sets of riffles for their 2" dredge.
3. Pump: 52 GPM is not going to cut it, even at 80% of throttle. 3/8" of water depth through a sluice processing nearly 2" material will not allow it to function properly (retain & discharge). Most of the major dredge manufacturers use at least 90-100 GPM pumps. You're also using a wider sluice, so that's another factor to consider. Not sure about multiple stages on smaller dredges. If you go that route you will definitely need more water.
4. Sluice Width: With the pump you're using, you're definitely at a disadvantage with a wider sluice. If you stick with that pump you may want to consider an 8" or 9" wide sluice. Most 2" dredges use sluices that are 10x36. Lots of R&D has gone into dredge sluices over the past 4 decades, so try to start with what is proven to work and adjust from there if possible.
5. Crash Plate: 15" crash plate is fine. Gold will drop through the plate quickly with normal dredging so there's really no reason to have excessively long crash plates in there unless you plan on hogging material or running really fast. If you go with 1/4" plate try to get a plate that is at least 60% open and keep your crash plate height between 5/8 and 3/4". You may want to consider 3/8 plate and 40%-50% open with 1" crash plate height, that seems to work very well on the smaller dredges. I think you'll have to reconsider the pump because even 3/4" of water in that sluice won't be enough to clear above and below the crash plate. Also consider low-profile riffles under the plate directly after the top mat. They typically start about 8"-10" from the top.
6. Guts: Sluice guts are more of a personal preference and you'll see dozens of variations being used. Just keep in mind that you want the gold to drop, stop, and hide as soon as possible. A small section of black ribbed matting up top is good for spot checking and is fun to look at, but it doesn't provide a whole lot of protection for gold (of any size). It also scours easily if rock jams or buildups occur. Definitely do not line the entire top half of your sluice with only v-mat. You'd be wasting the most critical part of the sluice. Most of the dredge sluices you see only have like 6" or 8" of black mat. You want to introduce riffles as soon as possible as well as carpet, moss, and expanded. As mentioned above, adding a couple low-profile riffles right after the v-mat and under the crash plate work well too, just be cautious about clearance (material over riffles under the plate). Putting raised expanded over moss or carpet works extremely well if low profile riffles are not being used under the crash plate. In a nutshell, use whatever provides the most places for gold to burrow down and escape the flow.
7. Sluice Adjustment: Absolutely make your sluice angle adjustable! Besides changing the way you dredge and controlling material intake rates, being able to adjust the sluice angle is one of the primary adjustments you'll need to make and is a must have.
Fortune favors the brave