Another way to do that is to make up a holding plate. An aluminum plate with all the mounting holes accurately located and drilled in it. Pre-drill and tap the five bridge blocks, then bolt them to the underside of the holding plate. This holds the blocks in accurate position in relation to each other while you set them into their beds of epoxy. You still lay out and rout the pockets in the body to get them very close to the correct positions. Try to minimize the clearance between the blocks and pocket walls that gets filled with epoxy. But the plate guarantees accurate positioning.
I also recommend that you use a screw in each bridge block to hold it down into the body wood, in addition to the epoxy. Pre-drill the screw holes in the blocks first, and epoxy them in using the holding plate. Epoxy may fill the screw holes, but that's okay. After the epoxy has cured, drill down through and install the screws.
I suggest the screws from experience: A few years ago, Keith and I did a prototype bass with an aluminum bridge block set in epoxy from the top. During testing, strung up, the bridge block popped out! That was embarrassing. The lesson learned was that the epoxy was doing a great job of making a tight fit; rigid contact between the aluminum and the wood. The block was a nice snug fit in the pocket. But the epoxy's bond on the aluminum wasn't that great. So it popped out. We popped it back in and added a couple of screws threaded down into the wood.
So I recommend epoxy plus screws for any bridge block that's set in from the top.
