Thanks for the Welcome. Well the front and rear seals are bad and blowing oil all over the road, 1/2 quart of oil per 100 miles.Gary said:Welcome to the forum first off.
Might I suggest you haven't told us what is wrong with the current 4.3,so it make it hard to suggest to rebuild it.The 1986 is a TBI if I am not mistaken,so that does give you a wide range of choices for used ones.You might want to take a look at this link to see pricing and availability at junk yards.
Now that brings us to the 350.Question is did you have other plans for it???.Seems you built it for a reason that didn't include a install in the Astro.What is the overall condition of the Astro comes into play as well.In terms of gas mileage with the 350,many report the same as the 4.3 or better primary because the engine doesn't work very hard to move the Astro.
Hope this helps and let us know what you have decided.
and yes it's a TBI
I had no plans for the '77 350 it was for a project that fell through.
The van is in good shape just the motor blowing oil. 112,000 miles
If I did go with the 350 I would just get an intake and tBI and chip from a full size?
Don't mean to ask so many questions but all the info I have searched was for newer models.