I have a warmish pinto in my mk1.
It was rebuilt before i bought the car.
Im not sure of the contents but has a decent cam. Was on a single dcoe now on twin.
Anyway it has a vented catch can. It is blowing a fair bit of fumes out of the filter, there is hardly any oil in the can though.
I have put a spring on the dipstick
After a decent drive when the motor is hot the volume of vapour increases.
This seems to have increased since i bought the car.
I think the mk1 is trying to kill me.

I ran twin carbs and oil catch can on my Pinto for years before removing the catch can to empty it, after all that time there was only a dribble of oil in it. I think the PCV oil separator is quite effective on the pinto.
 
I also had the original breathable oil filler cap on the engine which would also reduce crankcase pressure, however never had any issues with excessive blowby, there was some if you removed the oil filler cap with the engine running however never had troubles with the dip stick blowing out.
 
Has the engine been run in yet or is it a new rebuild? Piston ring sealing improves with running in.
 
You can perform a compression check and cylinder leak down test to determine the condition of the bores/rings/pistons.

I "think" it is a fresh build maybe 1-2k on it.
There is a tube from the oil filler cap to the catch can.
Ill see if i can get a leak down test done next week.
My concern is that it seems to be getting worse.