Look at the photos in your assembly manual. Yes, the original straps had sloted holes so they could me moved in or out to fit different width engines. You know what engine is going into your airplane so sloting is not necessary if you measure, and drill accuractly. Drill the 2 holes for bolting the straps to the wooden mount beams just a little larger O. D. than the bolt shanks, then slot them if needed to get them into the desired mounting position (so you engine just fits between the straps). Then position your engine for and aft, mark and drill the 2 holes per side to mount the engine (again the holes just a little larger than the outside diameter of the engine mount bolt shanks). "Tweek the holes as needed to get everything to fit and line up. I believe the beams come pre drilled for the strap mount holes but anyway mine measure 2 3/8" apart. I also made my replacement straps 3" long, not 2 3/4" like the originals. this leaves plenty of meat on each end of the parts and there is plenty of room for the slightly longer mount straps. Not much extra room anywhere else in this engine bay as is's a tight fit everywhere else! Not the easiest engine instalation you will ever do, it requires patience.