Get a fleming, qualified, or s&h sear. If it isn't installed in the type of trigger group you want have someone like tsc machine or s&h install it in a pack you want. You can then move it between hosts, for caliber changes you just need to change the ejector level and maybe the hammer spring depending. Setup your hosts with trigger housing that match how the pack with the sear is installed so you can drop it in them.
A double push pin would be a registered gun meaning you have the single machinegun. With a sear installed in a pack you can move the mg to multiple hosts like the 53 you want.