Andy...I do see a large clearance

between the OD of the split pin & the ID or the washer....which may be problematic for soldering...
[I suspect if you gauge your M2 washers, they may in fact be M2 clearance or approx 2.2 to 2.3]
I found the Germans as the only supplier of brass
hex head, but this guy in China for M2 & M3 washers, M2 & M3 S/S socket head cap screws.....and amazingly M3 socket head cap screws in brass!
I just search in Google/e-bay....find t
his supplier name & choose to purchase from him as there are usually 2 or 3 suppliers with the same product for same or similar cost
In the last image you can see the M2 HSS twist drill in the caliper & a sample of one of his M2 ID washers.....with very little clearance.....obviously they use 2.0 diameter pins in their die forming operations.........[not 2.2 like others]
[200 M3 brass washers were $5.36 Australian ..posted free to me].............
Derek