What workout to do on the Gym Spin bike? And use RPE or power pedals?

I’m just about to start short power build - low volume. I will add a fast Monday night chain-gang ride to the three prescribed workouts. This is usually 90 - 120 minutes and is hard to very hard. There are often a few Cat 1 and 2 riders that show up (I’m Cat 4) and blow us to bits by the end.

I have access to spin bikes in the work gym and could get upstairs for 1 or 2 45min lunchtime rides on them each week. I have power pedals I can use with these bikes too although if I do then it;s probably going to be a 40 minute workout.

So what workouts from the plan would be best suited to swapping out and doing as a spin bike session? I’m thinking that the two 45 minute workouts could equal one of the 75 / 90 minute workouts from the plan.

Also, is it better to go off RPE and get the extra 5 minutes per workout or take thhe 5 minutes to install and uninstall the power pedals?

A bit of background. I’ve trained with TR for a number of years but always followed sustained power / triathlon plans. My FTP from ramp test is a little over 4w/kg and my weakness is very much short snappy power. I did just complete my own modified version of Short Power Build, using workouts from both he medium and low volume plans but swapping out and skipping quite a lot in favour of group rides, TT and road races. I’m not entirely satisfied with my progress and want to start the short power build again. I didn’t do many of the anaerobic type workouts and feel like this is where my focus needs to be now.