Engine misfire bogging down under load

[UK67]

67 small block L79 engine.
Had a great day at Kop Hill until the drive home when for the first time in 7 years I really thought I was going to break down. Engine started to bog down under power and had to be gentle on the acc. pedal just to keep moving. After about 10 mins all was okay and I breathed a sigh of relief until it started again and remained for the remaining 10 miles home.
Any suggestions I'm thinking something ignition related maybe the coil?

 

[teamzr1]

Maybe fuel pump/pressure,
bad gas or fuel filter,
low battery voltage, or
ignition related breakdown under heat ?

 

[Oneball]

I think I’d start with ignition too

 

[James Vette]

Cars are very complicated. One thing goes wrong and everything goes wrong.

 

[Roscobbc]

Maybe fuel pump/pressure,
bad gas or fuel filter,
low battery voltage, or
ignition related breakdown under heat ?

Coincidentally it was during a Kop Hill run (half way up the hill run where the engine cut and I fought to get it to creep up the rest of the hill) that I realised that the mechanical fuel pump was on it last legs, presumably the diaphragm partly perished from the ethanol in our petrol (we've had it for far longer than many realise) - the pump would supplying sufficient fuel for normal running but when put under extreme continuous load and 'asked' to feed the engine under heavy acceleration for more than a few seconds it was draining the float bowls - the engine would start cutting out until some fresh fuel pumped through.