Which leg rests did you use? Sunrise told someone I know there are not 90° angle points for rear wheelchairs. Her DME stated he did not know any aftermarket ones either
Have no idea what that even means.
The only thing preventing 90 degree retraction on a rear drive chair is the rear of the footlates and caster tyres wanting to be in the same place. So it limits how far back you can pull in the footrest. You will never get 90 degrees.
Fitting smaller tyres, or choosing a chair with wider caster centre points, will still not allow full 90 degrees unless you have the seat too far forwards. Even swing aways are typically 70 degrees and thats with the seat a long way too far forwards. All ths complicatin is why every stock rear drive chair is so nose heavy. It takes a little effort to reconfigure things to make them steer properly and not feel long.
The seat frame is the same across all the Q300, Q400, Q500, Q700, in mid drive, rear drive, hybrid, and front drive. It literally bolts on with two bolts.
The actual types of centre mount footrests are all capable of 90 or very close to that. And there are non adjustable non powered (manual bolt in the position you choose) ones, ones that are powered in two different footplate lengths, and these can be long, short, and or extended so they can reach to the ground.
So in all about 5 or 6 types.
The one I personally have was for sale on the same website by same seller on eBay as the Q700 powerchair. It had the godawful power swing away ones fitted. I agreed with the seller to fit the centre mount one instead, and in the price. I made an offer. £4400 complete with the centre mount footplate. Chair was unmarked, and had single digit miles. All the expensive options, power everything, lights, 4 pole, 120A and CJSM2 and unwanted Gyro... Delivered with 12 months warranty. With centremount fitted.