Helped a buddy's son do this on his 1972 last summer.
He looked at several system, including the fancy sequential units, and then bought the Dakota Digital units from Summit (under $200 IIRC with the LED type flasher also ordered).
As noted above, you'll need a 'digital' LED type flasher driver for these conversions - you're standard 'load' type flashers will not work ...
The side markers are an easy plug in conversion using an LED 194 type replacement bulb.
These can be found at lots of local chain type auto parts stores or ordered from Summit and others on line.
Be SURE to check specifications to be sure they will fit and put out the required amount of light needed - some are pretty lame
Same goes for dash and other interior lamps in many cases, you can find replacement LED bulbs for many of the locations.
The indicators, door lighting. glove box(es) and others come to mind.