The proper way to know the correct size bass to play is while standing behind the bass in playing position, the fingerboard nut should be at the top of the ear, and the right hand should be able to comfortably draw the bow from frog to tip. The first and fourth fingers of the left hand should be able to easily span a whole tone (E-F#) on the D-string in the first position. You would need a 3/4 or possibly a 1/2 but I think that will still be too small. Keep in mind that the bigger the instrument, the better the sound. For the bass to have its best sound for its pitch, it really should be another 10" larger than the 3/4, but that would make it impossible to play by a human.
Engelhardts are very nasty quality plywood basses. Old Kay's as far as older plywoods go are a great choice for blue grass, and jazz, still not very good for classical. Here is some more info on ply wood basses and some modern well made ones..
• Plywoods tend to have a more 'hollow' sound compared to a carved wood bass
• Plywoods tend to amplify better, they sound better through the amp than acoustically
• Plys tend to put out less volume.
• Plys usually don't bow too well (sound-wise). This is where you really notice a huge difference.
• Ply basses seem to be generally set up with less tension (less string angle across the bridge) which makes them play differently.
• The dynamic range of plys tends to be a lot narrower.
• Plys tend to have a lot less clarity in tone.
• Plys tend to do better with pickups that compress a lot (Underwood, Fishman)
• Playing plywood after a wood bass is really a let down.
Thompson Plywood ($1500) http://www.stringemporium.com/thompson-upright-plywood-basses.htm
Thompson Hybrid ($2200) http://www.stringemporium.com/hybrid-upright-bass.htm
Christopher Plywood ($1800) http://www.uptonbass.com/Christopher-Laminated-Double-Bass-model-DB204T-2004/
Shen Plywood ($1500) http://www.uptonbass.com/SB80-SHEN-BASS-Samuel-Shen-Double-Bass/
Eastman model 80 Plywood ($1800) http://theviolincenter.com/Samuel-Eastman-Double-Bass-Outfit-Model-80-7-8-1-8-VB80.htm