bit late now maybe, but have you considered using R12?

I just did a redo of my 83 240D - new compressor, drier and flushed, with R12.

From everything I read, and the advice of a long time ex merc mech, R12 is the way to go. The 123s don't have a big enough radiator to cool effectively with R134. PLus R134 has higher pressure. Basically, it sucks. There are lots of posts on it, here and on other sites.

If you're set on R134, and you're doing it all yourself, consider Freeze 12 - it's basically 50% R134 and 50% R22 (I think), anyway, it cools better and is pretty much regular. Just don' expect a auto shop to like you if you bring it in for service - they probably won't have the equipment to officially deal with it.

Also, for vacuum, I vacuumed my setup with a compressor I took out of an old fridge from a junkyard. Cost = $0. Vacuumed to 26 " HG and then let it sit to check the vacuum held.

I wouldn't trust a harbor freight pump to do too well myself.....Some of their tools are OK, some suck. I was going to use that same air operated vac pump - actually, I bought one, but took it back after I read about what a pounding it puts your air compressor through.

You can buy R12 on ebay for about the same price (maybe a littel more) as R134. I believe you need 2.2 pounds for the 300D - less than 3 cans.

That's my 2c. If you have any questions, let me know.