Hi John,
If your only going to change out the Lifters then the easy option as suggested by an earlier member is to buy adjustable pushrods, cut the old ones off with bolt croppers (if you don't have croppers use a cutting disc, carefully making sure nothing goes down the lifter bores), if you have not decided on the lifters, go for the S&S lifters (without HL2T kit), do not buy new Harley ones.
If you decide to go the removing the rocker box route, get a good quality allen wrench (the rocker box bolts have a allen wrench fitting and also a standard imperial hex bolt head) and using a Dremel and fine cutting disc cut it down so it protrudes just enough from the bolt to enable you to get a small ring spanner on it, you can also get a little extra room if you undo the front motor mount bracket from the front of the engine, but make sure you support the engine.
As suggested earlier while your in that deep you may want to change out the inner cam bearings (a major source of problems with these engines, if they break they often cause major damage) it means removing your exhaust, cam cover and the removal of the camplate with cams, if you have a workshop manual its not as difficult as it sounds, you will need a cam bearing removal tool and installer.
Its a time consuming fiddly job, you just need a little patience, Good luck.