Port Glasgow to Linwood..
parts of track (Tarmac excellent surface) esp in urban areas prone to odd glass hot spots, middle Port Glasgow esp, under bridge at Bridge of Weir, after Paisley Canal station, track goes through mostly parkland with occasional glass. Road Bike wouldn't be a problem on this part.
Glengarnock to Linwood ,
another cracking tarmac surface, two road crossings enroute, 75 joins at Linwood, track then to Elderslie, short road stretch then back on another excellent tarmac track until Paisley Canal station, short park section, now 7 winds its way through a built up area, then a mixture of parkland, roads, some parkland bits still okay for road bike but not silky smooth.
A fair haul, mind you.
Port Glasgow? all literally downhill to Linwood, approx. 400ft on return journey but not really noticeable..
Glengarnock ? pretty flat the whole way..