Yes. JBL305 could be regarded as near field monitors.
Distance? I think this will depend on personal preference and desired SPL rather than following a hard and fast rule. With 7" cones you would certainly get away with it, 4" cones maybe not. 5"? I'd guess you'd be good but experiment if you can. The important thing is to maintain the equilateral triangle.
If you have the freedom to arrange the room for audio it's best to start from the optimal listening position. This is usually in the middle, 1/3 of the way down the long side of the room. Then place your mains if possible 2' away from any wall and then construct the equilateral triangle from there using the optimal listening point as the base position. Provided you have the SPL it should all be good.
The second best listening position is now 2/3 of the way down the long side of the room. So you will excellent near field and pretty decent mid field.
The next step would be to put some bass traps in the corners and acoustic panels at the primary reflection points i.e side walls, ceiling and floor (rug?) around the primary (and secondary if you can) listening position. If that's not clear there are many guides available if you do a search.
As a guide I found it suited me to have my 4" monitors mounted on stands on a desk ~40" apart. The 5" work better slightly further apart mounted on full height stands just behind a desk or table. Twin 7" mid/far field as far apart as possible whilst maintaining the equilateral triangle based on the optimal listening position and distance from the corners. Remember, from an acoustic perspective, your room has 12 corners not 8 if it's rectangular..