How extensive you you looking to go as far as a "rebuild kit" just gaskets and seals, rings and bearings?? AS far as gasket sets I haven't seen one yet that comes with the head gasket as there are 3 different thicknesses which require measruing the piston protrusion..
Best way to determine if you have mech or hydro lifters is to look for the extra bump. Engine block code will work too.. '86 was to be the official changeover year to hydro lifters, but IIRC I have heard some reports of '85s having them.. And of course there is also the factor of things getting swapped over the years... The head with the smaller drain back hole plugged was probably installed, or to be installed on a mech lifter block...
AS far as mech vs hydro, there has been debate on the subject in the past.. Some say they felt as though the mech engines made a little more power, but nothing definite... The nice thing with the hydro head is there is never the need to adjust valves, which can be a pain..