74 dart sport msd 6al

If you already have the 6al, go ahead and use it. If you don't have one, and your motor is stock, or mild build, do the HEI conversion. The HEI can be done for about $50. You can use your stock distributor. You will not have rev limiter capabilities, it is not really needed with a stock or mild build. Also the multi spark is really not needed, and it only works below 3,000 rpm, anyway. The HEI will throw nall the spark you need.
PS: If the MSD should fail, it won't be a cheap repair/replacement, If you can get one where you are when/if it fails. If the HEI should fail, any auto parts store should have the parts.