If I were you and I had absolutely no mechanical knowledge, then I'd get the disc brake conversion (say about $1500 to $2000) done professionally and learn all I can about doing my own engine. Like Aaron of this forum said:
(In my best Aaron impersonation voice) "If you ever played with lego when you were a kid then putting together an mini engine is the same. Consult a few books, find out a few tips, ask a few mates and hey presto..." (not exactly word for word but pretty close

)
It's the best bang for buck, cause at the end of the day when you run into problems, you'll know how to fix it. Esp if you are not looking to hot up your engine. That's my honest opinion. Go on, you know you want to! just takes balls to immerse yourself into it!

Least that way you know you aren't getting ripped off and probably have change left from $3000 or so. I am willing to bet that your current engine will last you at least another 6 months (if driven nicely) which is plenty of time to learn all you can about the A series...
Actually I lie, IF i were you I'd do it all myself
