If ya got A/C its gonna be a pain, at least in my truck it is, to get to the heater core, you have to pull out the cooling unit as well, which means discharge, evac and recharge...nothing more than a trip and some added cost with 134a, but if you have R-12 its prolly gonna suck. i had a hell of a time finding someone to just take what little R-12 was left when i converted to 134a due to a leak, and since you're opening the system, you'll need o-rings and a new accumulator at least, i believe the ones they sell now will work with the old r-12...finding oil for the r12 system i dunno, hopefully your system is in good shape and the shop can just throw the old back in. Other than that its pretty straightforward, get a haynes manual and you should be good. remember to bleed the air from the system when yer done, also recommend flushing and replacing antifreeze and any old hoses while you have it apart with summer around the corner. Good luck!