Your times are very similar to mine, when I used to run for Hercules Wimbledon AC back in the late 70s and early 80s. My times: 8:57, 15:12, 32:22, 52:03, 1:50.49 (3000/5000/10,000, 10 miles, 20 miles ).
The 20 mile performance was recorded in the Finchley 20 on April 22, 1978. I wore Tiger Onitsuka plimsolls in that race with absolutely no padding.
Basically I was on about 50 to 60 miles a week, no track training, and on Sundays I was usually doing a 15 mile run starting in Wimbledon and going over Wimbledon Common and into Richmond Park. Most of my runs were progressive runs during the week over about 7 to 8 miles. I would start off steady and try to finish “eyeballs out” close to six minutes per mile or even under. That was my method. Consistency was the key and frequent racing which counted as speed work for me.
On long runs (Sundays, 10-15 miles), I would usually start off steady at around 7 to 7 1/2 minutes per mile and usually I would try to finish the longer runs at a faster pace down to around 630 per mile, or faster.
In those days I used to race almost every week so those mid weekly races for example on the track at Crystal Palace or at West London stadium counted as speed work because I never did any speed work on my own.
My best performance in the national cross country over 9 miles was 250th in 1978.
In my club we had people like David Clark, 13:22/27:56 for 5000/10,000 m on the track and English cross country international, and Bob Holt 13:48/28:39/ 48:00/2:16. I was just an average runner for Hercules Wimbledon and was lucky to make the nine man team for the national cross country. My best place in the Surrey County cross country was 26th 1979. In the Surrey league division one, my best placing was 22nd. Standards were high in those days with plenty of internationals running all those races.
There were so many good runners in those days if I ran a race like the Woking 10 mile race in 52 minutes I usually only finished around 40th. The top 10 runners would mostly all be below 50 minutes. Standards have gotten much softer over the years. Good luck.