I have a 300 D, and just sold a 300 TD.
Rough idle is pretty normal for 30-45 seconds. It will remind you of a tractor when it first starts. If it starts with one glow cycle, the glow plugs are probably fine, and the warm up cycle is normal. When it is cold, two cycles help. (15 F and below)
Smoking is normal for this time, but goes away quickly.
I highly doubt any of your glow plugs are bad, as just one bad makes these very hard to start.

A little smoke when you floor it is normal too.
87 is a real mix of old and newer tech. Aluminum head, but purely mechanical.
Make sure your cooling system is in top notch shape, and so long as it never gets overheated, the 603 will serve you well.

Check the tensioner and spring carefully. It should be pretty much parallel to the engine block. If there is much of an angle on it at all, its time to replace it. The plastic tanks on the radiator get brittle with age.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes