rebuild 13-B, have rebuilt, or buy reman?

[bowjangles]

I could use some advice; Here's the problem:
I have an old '74-75 13-B in my '80 Triumph Tr-7 roadster. it is non-turbo with a Hitachi 4bbl carbeurator;

Recently, it has started to smoke like crazy when I start it up.The smoke screen lessens after running awhile, but never goes away completely.
I can't tell whether the smoke is from coolant or oil, but after reading many forums, I'm pretty sure that the engine is toast-Sounds like coolant or oil seals are bad? Wish I was wrong!
Is there a way to determine the cause of the smoke w/o opening up the engine?

So, what are your thoughts about whether I should;
#1 Rebuild the engine myself-Have never done this to a Rotary, but have rebuilt other engines.
#2 Find a rebuilder. I have a list, any recommendations?
#3 buy a remanufactured engine -Don't have any sources for this.

Time is not an issue here as I am retired, but economics is important to me.