If your 72 engine is the matching numbers engine for your car, don't even remotely consider selling it. Either rebuild it or store it safely and rebuild the other one. (I'd do the latter for a stroker, and the former for stock displacement)
I would not bother having machine work done to a stock crank nowadays.
Have a pro (Geoff Hauser, or John Webster, Dave Billadeau, take your pick) give you a quote on the following work for your spare block :
- tank cleaning,
- Bore +30,
- New cam bearings,
- oil pickup gallery enlarged to 1/2 (you can do without, either if you don't plan to race the car, or if you will be using an external oil pickup - but the latter is not 'budget'),
- crank centerline bore/hone
compare this to the price of a fully prepped block (from 440source.com for example.)
http://www.440source.com/blocks.htm
http://www.440source.com/blockinfo.htm
Shipping will probably not be cheap though.
Then, look at the stroker kits (you may keep the stock displacement if you choose to do so) :
http://www.440source.com/strokerkits.htm
which will bring you 500+cubic inches, brand new light rods, all balanced, for about the same price as a set of pistons and machine work on your old crank.
The 440 source rods are much lighter and stronger than 6-pack rods (the rod+piston+pin assembly is 25% lighter than the 6-pack+OEM piston assembly - my engine revs like a small-block).
You did not say what you wanted to do with your car.
Basically, if you just want to rebuild the engine for street and highway use, rebuild the 72 block, stock displacement, stock or near stock camshaft.
If you want to play at Santa Pod, go for a 543 stroker kit. The price is the same, and all you need is a camshaft (may I suggest this one :
http://www.straightline-perf.com/dyno-ehead496.html - it's the camshaft I have).
Heads : there again, unless your heads are in exceptional condition, don't even bother to have them machined for unleaded, new guides, etc.
Get new aluminum ones. Edelbrock are relatively cheap and can be mildly (or wildly) ported depending on what you want.
Bigger than that (Indy) will not be budget.
http://www.outrageouslyvintage.com is the place to go for Eddy heads (actually, there are many others, but this is a nice joint).
If you're not in a hurry to get things done, 440 source will have new heads soon (early 2008 I suppose). And a block is in the works too, but don't hold your breath for it.
Settle on the head type you will use before picking the stroker kit, you'll need to know the chamber volume to choose your compression ratio.
Then you'll need a new oil pump, a complete gasket set, a timing chain, etc. Most of that stuff can be found on 440source.
Start by browsing the entire 440source website, and start an Excel spreadsheet with the price of everything. Evaluate your options (mild/mixed/wild). Ask more questions.
I also bought some stuff from Chenoweth Racing, they also have machined blocks, you might want to check them out.
You did not say if you were going to do the work yourself or have it done.