I found a set of 351w heads for 50 bucks. They are "T" cast heads from 94. The valve size is 1.78/1.46. Will this be a good enough upgrade over my stock 289 heads? Are the springs heavier than stock 289?

Of course I would shave the head for proper compression.

 

not sure on the specifics of the 94 351w head, but I would mount it on the engine and do a valve clearance check using putty/clay before you shave the head too much.

 

They are not an "upgrade" over stock 289 heads at all...Especially if your 289 heads are pre 1968s...In fact you will lose alot of compression and gain nothing else..

 

yup, not getting them.