Misfire Under Load

[Spyglass]

I recently bought an ERA with a 428, it's 5 years old and has approx 3,000 total miles on it, I understand the engine build is:

Believed to be a 1968 block
Scat 4.250 rotating assembly, 462 ci
Mahle forged Pistons
Edelbrock Performer RPM heads
9.5 to 1 CR
Edelbrock intake
Holley 750
MSD distributor
Howard hydraulic roller cam
Harland Sharp rocker assembly
Canton road race oil pan

I've driven the car approx 500 miles and experienced a progressively worsening oil leak(s) and misfiring under load. The oil leak(s) appear to be coming from the upper front drivers side of the engine, I've replaced the fuel pump gasket and managed to get 1/4 turn by hand on the remote oil filter, both of which appeared to be culprits. I haven't driven it since to know if this has cured the leaks.

The misfire is of greater concern, the engine starts, idles and runs fine at light throttle applications. However when I accelerate harder, say 1/2 throttle and 2500 to 3000 rpm the engine starts to misfire/stumble, it will continue to pull through the misfire. On the few occasions I've accelerated at full throttle, it again misfires/stumbles, then appears to clear itself and when I look in the rear view mirror there is a large blue cloud of smoke in the road. I don't think this is a constant trail of smoke, rather a single cloud that's blown out.

Apologies for the very long post, if you've managed to read this far, do you have any ideas or suggestions as to what's wrong?

Thanks in advance for any assistance.
Regards
Kevin