Absolutlely leave them a bit loose if you are unsure. I don't trust my valves unless I can hear them slightly. I have a straight six BMW with 155k miles, an inline 4 motorcycle with 45k miles, and my stovebolt with who knows how many miles, all with solid lifters and mechanical adjustment, and all running perfectly smooth with slightly tapping lifters and absolutely no valve train problems. The BMW won't pass emissions and gets bad gas milage if you set them too tight, stovebolt and bikebolt are exempt.
