New Owner with questions

[DBG]

Just bought 1978 V20 Steplift with Mercruiser 470 I/O.

Does anybody know where to get a manual? Also what is the normal operating temperature of the Merc 470? I took mine out on the water and it was running at around 160 at idle and 200 on plane. And how do I replace the raw water impeller/where is it located? Any answers will help. Any tips on care or what to expect to break would be appreciated. Thanks!