Well, with the casting number, that helps narrow it down.
I checked a couple of other sites and your son's info is spot on!
Well done!
Now, here's an additional little bit of info, '86 was the first year of the roller cam small block!
From the casting number, your engine is a truck engine, so will have a roller cam (and will accept any SBC roller cam, GM or aftermarket), however the lifters will be regular hydraulic flat tappet as will the remander of the valve train.
Some of the early roller cam SBC's had 'bosses' cast on the cam tunnel, that can be drilled and tapped to hold the 'lifter tray', that keeps the roller lifters straight.
A search for a 'how to' will yield a number of results.
So, with the block stripped down, it can be modified to a full roller valve train.
Chevy has a number of strong GM roller cams that can be had (used condition) through wrecking yards for cheap.
Well, leastwise on this side of the pond.
That block can build a very large amount of HP and torque, for cheap.
Chevy has several series of factory heads that flow very well.
You mention gas is £1.40 per litre in your area.
I am planning a holiday either late this summer or late next summer, to the Isle of Man.
I live in south central Texas, so it's going to be quite a trip.
I would love to go for the motorcycle races, but don't enjoy the massive crowds and jammed accomodations, so we'll be going after the races, probably in August.
I found an agency (Manx Mini Adventures see link below) on the Isle, that hires classic MInis for £70 per day between May and September, £60 per day from October to April, of course + applicable taxes.
Then I did a search for gas prices on the Isle, looks like £1.55(IMP) per litre!
So, I guess I'll be bring my petrol with me from Liverpool on the ferry!
Save 15 pense per litre!
http://www.visitisleofman.com/thingstos ... ntures.xml
Keep us posted on the progress with your roller cam 350 vintage pickup!