Floor preparation for paint
With the welding, grinding and sanding behind me it was time to prepare the floor to accept its first coats of paint. The entire floor was acid washed with POR15 Metal Ready. Several costs were applied including to all joints with a hard brush and 3m Scotch Brite pad until all signs of surface rust were removed. The acid was continually sprayed with water from a plastic spray bottle to keep the acid from drying and to reactivate it. After soaking in acid for 20 minutes the floor was thoroughly washed down with warm water and immediately dried before any rust formed.
The dry floor was then sanded with 3m Scotch Brite pad and cleaned with panel wipe and degreaser. I used a Devilbiss GTI gravity feed gun with a 1.4mm tip to spray the floors with three coats of PPG DP40 epoxy primer. This should provide sufficient coats to seal the metal over which was sprayed 3M smooth anti chip coating, Grey part number: 08886. I like this product as it is smooth and overpaintable and sharing the same, robust anti-chip benefits of the textured product, 3M™ Smooth Coating dries rapidly to an excellent finish. Applied using the pressure adjustable air-fed 3M Pressure Pot Stonechip Applicator gun gives the best results.
The floor pan joints were seam sealed with Wurth Polyurethane adhesive and sealing compound. Product 0890 100 2 Grey using a hand application gun. A further coat of PPG DP40 epoxy primer will follow three coats of PPG Semi-Gloss black DB167 or RAL7167 (DB164 or DB167 Tiefdunkelgrau Matt). 
The paint codes quoted from Mercedes-Benz documentation supplied by the Classic Centre were:
DB-Nr. 167 oder RAL 7167 (tiefdunkelgrau - low dark gray)
MB teilenr. A 00 986 67 33/7167
The 190SL Group technical manual quotes this as A000 986 67 33/7164.
Looking at the Glasurit Color-online both these codes MB7167 and MB7164 come up as Tiefdunkelgrau Matt.
I had my local paint supplier mix up the DB167 RAL7167 and it looks very close to the original colour from the flap below the fuse box cover and is not Matt but semi-gloss.
Wurth list in their catalogue the MB167 as an aerosol 400ml can code number 0893 349 167.