Diplomat project

In 1985 my V8 was scrapped with all conceivable extras by an unindebted accident.After decades of abstinence, I acquired a Diplomat 2.8 E from 1977. 1 year TÜV, H-mark, stainless, inside like a 5 year old car from 2nd hand. The aim is to upgrade the car without changing the original condition. At least the condition should be recreable. So no further holes should be drilled and the like. retrofit it, upgrade the level, upgrade the mirror to the right, install the AHK, install the ZV if necessary, add-on instruments. Sliding roof is not available. It is also planned to replace the seats, currently good blue velour seats, with others.Perhaps individual seats in the back.The original seats must be mountable again. Who has experience with such works? Here some pictures of the current condition. The car is also suitable for everyday use. Has survived over 800 KM at a time.