It's a myth that if you don't have mufflers on your car that you will damage the engine. In the old days, we would put cut-outs on ours, then when race day came, we would open up the system just after the headers. We increased the horsepower that way. Same holds true today. However, it is against the law to run straight pipes, so my suggestion is to put some flows on there, then put cut-outs on it to open up the system when out on a lonely country road.
I also grew up on an irrigated cotton farm where we ran GM motors to operate our water pumps back in the 60's. We did not run any mufflers on those engines which ran night and day for 5 or 6 years at a time without overhaul.
