You assume a lot. My dislike of hydraulic lifters of any kind, Rhoads or otherwise, comes from the fact that they are an inaccurate way to actuate valves. Most hydraulic lifters have a plunger range of about .100" or so. Some more. As a result, you never know how much those plungers are moving. Are they all the same? Hardly. By contrast, when I adjust the valve train of a solid lifter camshaft, I can adjust each rocker arm to the same adjustment across the board and there's no variation. Solid lifters are more conducive to efficiency and that means benefits for power and mileage if you choose a camshaft for mileage. The adjustment is more stable. Instead of the variation of a hydraulic plunger moving around to the tune of .100" plus, you have valve lash adjusted on all 16 to a much more tight tolerance. I don't like Rhoads lifters because they move around even more! That's their design. "They say" full lift and duration is restored by 4000 RPM. Is it? What's their proof? If my engine is going to make ticking noises, it's going to be with a solid lifter valve train where I can measure the clearence, not with a hydraulic plunger where I have no idea of preload amount. Sure, there are "short travel" lifters and the like, but the Rhoads lifters go the "other way". They are long travel lifters by design, unless you use the V Max. Then you can adjust the amount of preload, similar to a solid lifter. Supposedly. And that's the problem "for me". You cannot "measure" how much lift you may or may not have on a running engine due to lifter plungers moving around. Hydraulic lifters were invented for only a couple of reasons. Noise and to eliminate the need for adjustment. That's it. Performance and efficiency were not considered. Go ahead and use them It's your engine. My personal preference is I would not. ...and yes, I've used them in the past on customer builds because they insisted on the "new and shiny" thing they read about in the magazines, but there was always "somewhere" in the engines RPM range where they felt disappointed. They were all used on very mild cams, which IMO is not their intended purpose. Are you going to be happy with an engine that gets 20-25 MPG but won't pull a greasy string out of a cat's ***, or would you rather have something that's at least a little fun to drive? The 273 is kinda like the slant 6. It needs all the help it can get. I would just build one with the standard 273 compression, not Commando and put an Edelbrock 500 on it. Use that little solid cam @toolmanmike is so fond of.....what is it? The E4? Put headers and good flowing dual exhaust on it and call it done. Easy peasy.