Q: Should I flush the evaporator that's still in the car?

Background: I'm in a middle of a mid-scale AC reclamation project, and I'm a newbie, but I'm determined to get it done, even if it's going to cost me. AC wasn't working when I bought the car last fall (the AC belt was gone), and a later check showed that all refrigerant was gone as well. There's no conclusive evidence regarding an R12->R134a retrofit. The only evidence is a single quick-connect R134a coupling -- the kind that screws on top of an existing R12 valve, no stickers of any kind, and no PO to ask. The quick-connect coupling is the low-side kind, but it was attached to the high-side valve (being new to the whole AC business, I haven't realized it right away... a bit scary). Practically no oil left in the system -- when I removed the compressor and put it vertically to drain oil, not a single drop came out (a couple of drops came out while I was unscrewing the compressor manifold though). Furthermore, I made things that much worse by screwing up UV dye injection: I had the system evacuated, at 29" vacuum, and attached a Mastercool 10-application concentrated UV die applicator can. The can has a rotating bottom, sort of like a deodorant stick, and the idea is to rotate the bottom one full turn to inject one application worth of die. Well, I plugged the can into the system at vacuum, and it turned out that one doesn't in fact need to turn anything, vacuum will suck in dye without my help, and by the time I realized that, about 8 applications worth of dye went in. So I think a good flush of the AC system is very much in order.

I started taking the system apart and flushing hoses. It doesn't appear like there was much dirt inside, aside from the bright yellow UV dye color, AC flush remains transparent. No solid particles came out. After flushing manifold hoses, I decided to take a leap of faith and flush the condenser while it's in the car. That wasn't a very encouraging experience. I'm using a Mastercool flush gun, and it seems to work as well as a flushing device should, but getting all of the flushing liquid out with the condenser sitting vertically in the car seems hard. I've been blowing air through the condenser for a while, and it looks like it keeps blowing out small amounts of liquid. I'm using special AC flush, and that stuff evaporates a lot less easily that I though it would (I was expecting something like non-chlorinated blade cleaner). I still think that blowing air through the system long enough should get all of it out, but I'm not positive anymore.

With all this in mind, I'm not very enthusiastic about flushing the evaporator (and well and truly reluctant to remove the evaporator just for the flushing). On one hand, there could be some old oil in there (wouldn't be much if there was any though). On the other hand, what if I can't get all of the flush liquid out of there? I've diligently read many, many prior articles on the topic, and I've seen different opinions expressed on the issue of flushing in general and flushing the evaporator while it's in the vehicle. I fully agree that a thorough flushing is a Good Thing, but then having AC flush left in the system would be not so good. Suggestions?

I'm going to put synthetic POE (Auto 100) oil in when I'm done (7 oz sounds like the right amount for a fully flushed system). The plan is to start by putting in R-134a, to see whether the compressor is alive and find any remaining leaks, and then sometime later, when I get some level of confidence in the system, replace it with R12, keeping the oil. Is that a reasonable approach?