Need help re-installing distributor on 450SL

[winecountryone]

I removed the distributor to replace the oil seal that has caused fouling of both the ignition and trigger points 3-4 times over last 2500 miles or so on my 1974 450 SL.I thought I had marked the distributor so I could put it back in same position but was apparently off somehow as the car now refuses to start.
I need to find/verify the proper procedure for finding #1 TDC so I can then re-install my distributor.I haven't had to go through this on any car for a VERY long time.This is what I did:
#1: removed the #1 plug and rotated until I could see/tap the piston through the plug hole.
#2 I then lined up the TDC mark on the crank pulley.
When viewing the cam lobe through the oil filler hole at this position,it appears that the intake valve lobe is pointing "down",thus depressing the intake valve.If the valve is open,then I'm obviously not at TDC on the intake stroke am I??
My mechanic is 60 miles away and doesn't do "house calls".Any help from forum members who could help get me back on the road would be greatly appreciated.