I wear a GQ 350 parachute in our RV-8 for some flight profiles (mainly displays/practices) - mainly "seat back" type, but some of the chute is "seat". I tried a few, and most pushed my back too far forward, especially low down. I leave the bottom cushion(s) in place, and remove the (front seat) rear cushion.
"I modified a stock seat back with a bend in it to make the seating posture more comfortable." Ditto without being aware of what Steve did
Is better... however, it does require the rear stick removed to full forward deflection. So swap seat backs for 2 up flying.
There are some "rules" re parachutes drilled into me over a flying career (or by others who have much more experience):
Parachutes can be ruined in a short time by being stored incorrectly. Apart from the very occasional overnight stay, that means removal from aircraft and storage in a suitable environment after flight.
You should, post flight, unstrap from the aircraft and exit with the parachute on - if you routinely disconnect the parachute then you will do the same reflex action under severe stress should you need to "jump". If the chute is being used again a few hours, climb out with it, take it off, put it in aircraft.
I have enough doubts you could abandon an RV-8 from the front seat. I have severe doubts you could from the rear seat, especially if the front seater has "gone".
Also agree with Paul's comments on straps.
Through unfortunate / tragic events, much of the above has been learned. Also, little point in wearing a parachute if you do not wear a helmet. The helmet is more likely to be needed in typical accidents, and keep you conscious enough to deploy the chute as you jump out and bang the tail etc.
Link (
http://www.mod.uk/NR/rdonlyres/7EFF...AC1F/0/maas85_03_bulldog_t1_xx660_25mar85.pdf ) - successful "jump" but undid parachute harness as well (reflex action) = fatal. This accident resulted in after every flight you climbed out with the chute on, removed it alongside the aircraft.
Link (
http://www.guardian.co.uk/lifeandstyle/2011/aug/12/i-crashed-vintage-plane/print ) - successful low level abandonment (<1000' mid-air)
"There was a deep gouge in my flying helmet – evidently, my head had bounced off the tail as well does not sound like he would have been in a good position to deploy the chute if he had not been wearing a helmet?"
From a recent (fatal x 2) accident, it has been highlighted (yet again) that owning and wearing a chute is but a small part of the "solution". You must have clear ideas/rules about when you will use it, the procedures (and calls / liaison if 2 occupants) to get out, the minimum heights for commencing abandonment - derived from that specific chutes "min deployment height". And such egress drills rehearsed regularly (monthly?)...