Back up here first.75 seems too be good to be true and usually is then.

There are oem blocks with the spider bosses drilled and tap that where not roller hydro's.A prime example is my 1995 383 block that was a flat tappet hydro.Well honestly 1995 was a transition yr so they came threw both ways.So the short answer is yes you use your stuff.

But..............you didn't say if your block was decked or the heads where cut.That could effect push rod length.
Oil pressure or low pressure is a effect of a bearing issue/oil pump issue and not a bore issue.So to reuse your two pc seal crank(again you need to tell us if your block is two pc or one pc seal.Saves us from running after casting numbers)in a one pc seal block requires a seal adapter.So add another 80 to 125 to the price of the 75.00 block.Then getting back to the oil pressure issue,tearing down your block you might find your going to have to turn your crank 10/10 anyways.At that point you current block and it's reuse isn't looking to bad of a option providing your bores don't need much other than hone/ re-ring.Again oil pressure is a function of bearings clearance/then oil pump.A stuck valve in the oil pump "could" provide low oil pressure at idle.

Spraying that little I would want atleast a upgrade on rod bolts.Yep-guys spray that little without ARP bolts,but not on my dollar.The cost benefit makes it silly to do without the better bolts.

The question about the stroker is for one thing the cam you have you might find it is about right to the increased C.I.'s because the 383's will accept a bigger cam more easily then the 355.I own a Howards stroker and I am sold on Howards products.American made and machined and a quality pc.Internal balance that may require Mallory metal.The point of the 383's is the greater torque curve at a lower RPM which what you want on a street vehicle.A major portion of ET is the first 330' where that torque curve plays a huge role.

My advise to you is to tear down what you have first before any $75 dollar deal to see what is the problem with the oil pressure and take a look at the bores,etc to asses the costs.

Also-I agree that Richard is very knowledgeable.The thing is Pat has been in the business of building engines for yrs as Jerry has and has hands on experience.If I where you,I would listen to either of them very closely.They tell you alot in one sentence.