The letter templates you bought were meant to be used with the guide template system kits. The template kits you are talking about include the rails, guide bushing/bushings, the base plate for use with the bushings and router bit/bits for use with the letter templates. They also include the letter templates. The cheaper of the two systems is for 2 1/2" letters and the larger kit is for 1 1/2" and 2 1/2" letters. Both sets include low profile clamps to hold the guides on your project while routing. These were all meant to be used as a system.
That being said you can use the character templates you bought without buying the guide template set but you will need the correct size guide bushings and router bits for your letter templates. You can make your own guide rails to hold the letter templates and figure out a way to clamp the guide in place, possibly build it into the jig. The guide rails need to be made so that the letter templates are held securely and do not move around during use. Not having the lettering templates I'm not sure how the rails need to be machined to hold the letter templates or if some metal extrusion can be bought that would work or be modified for use. Remember the letter templates need to be held where a guide collar will ride on the inside edge of the template to work correctly.
The big question is, knowing what you need to be able to use the templates, is it worth making your own guide rails and clamping system and buying guide collars and router bits to use with the letter templates? Will your router base accept guide collars or will you also need to buy or make a new base plate to use guide collars? Remember the guide template kits contain everything you need except the router.
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