All the small Nash L-head parts interchange. It started out in 1940 as a 172.6. Stroke was increased by 1/4" and it became the 184 in 1950 (172.5 was still made for the Rambler line). Stroke was increased by 1/4" again in 1952 to create the 195.6. Bore on all three sizes is 3-1/8". All used forged crank and rods, cast aluminum pistons.
The only major difference in any of them is the water pump. 1940-55 models use a water pump mounted on the left side center of the engine driven by and extension shaft on the rear of the generator. 1958-65 models use a front mounted water pump. The
1965 only block and oil pump is different -- it had a full-flow oil filter. That pump will only fit that block -- there is an additional oil passage in the bottom of the pump that mates to a matching port on the block.
The only thing to watch out for when swapping heads is compression. That varied over the years. Combustion chamber sizes are smaller for the smaller engines. If you use a small engine head on the bigger ones compression will go up, and vice-versa. Most of the small engines were low compression, so that's usually not a problem. The original 172.6 only had 6.87:1 compression (raised to 7.32:1 by 1955). The 184 had 7.0:1. The 195.6 started with 7.45:1, 8.0:1 for the dual carb. There was no L-head six made in 56 and 57. It was reintroduced for the Rambler American (a slightly modified 55 Nash Rambler!) in 1958. That's when the water pump location moved to the front of the engine and compression was raised to 8.0:1 (and stayed there through the end in 1965). The Edmunds heads are "high compression" and raise compression by about 1 full point. The early 172.6 head on a late 195.6 might raise compression more than 1 point, you'd have to measure combustion chamber volume.
The Statesman 195.6 dual-carb head was only made for 1955 models. 8.0:1 compression, two Carter YH carbs, 110 hp @ 4000 rpm. Edmunds and maybe Fenton made heads for all three.
