First off these engines redline at 3600 RPM so the numbers on the IP do not mean RPM. (Post a pic of the IP model number tags as the numbers don't make sense.) Some try for a whammy by taking an IDI out to 4000 RPM. They hated to be run past redline new, and with weak 20+ year old valve springs it's something even I won't do. Even with the newer engine you have, unless they raised the GM redline, I wouldn't take over 3600 RPM. Offhand I don't know if loaded under power redline is different then the higher compression braking RPM like the gas engines of the era have. (That would be the orange area on the tach is for compression braking.)
Your water pump is wrong if the pulleys don't line up. I don't know what the marine water pump uses. The older 6.2's were V belt and normal rotation. The real PIA is if you have a normal rotation pump you will need to also replace the timing cover the pump bolts to to get the reverse rotation serpentine pump on. It will be clear when you try and match up the proper pump to the cover if you need to replace the timing cover. Note: HO and normal pumps do not make any difference on the timing cover.
Single stat off a 6.5 works with a HO pump. Old 6.2 single stats don't fit well as I recall.
Your water pump is wrong if the pulleys don't line up. I don't know what the marine water pump uses. The older 6.2's were V belt and normal rotation. The real PIA is if you have a normal rotation pump you will need to also replace the timing cover the pump bolts to to get the reverse rotation serpentine pump on. It will be clear when you try and match up the proper pump to the cover if you need to replace the timing cover. Note: HO and normal pumps do not make any difference on the timing cover.
Single stat off a 6.5 works with a HO pump. Old 6.2 single stats don't fit well as I recall.