my 440 block came from a 77 truck.the flex plate has a window on each finger.my buddie gave me a 440 flex plate he got from summit.it is solid plate all the way across,so it must be stronger.the only difference,is that the holes on the ends are slightly larger than the ones on the stock flex plate.should i have any concerns using the one from summit?

There really isn't any "strength" diff. The holes in the FP on the ends ? ... there IS a diff on the size of the converter bolts.

With the exception of the Hemi, all converters use 5/16" drive bolts. Aftermarket flexplates will often have 3/8" or 7/16" bolt holes (7/16" is the Hemi size).

Not a good idea to use the small bolt in a larger hole but some get away with it.

Sounds like your buddy gave you a SFI rated flex plate. It will have larger mounting bolt holes. DO NOT use this plate with the smaller bolts used on an OEM flex plate. If you insist on using it either get a different converter or have the lugs drilled a tapped to accept the larger bolts. Most lugs will easily take that little over bore and still be plenty strong. If you use the small bolts in the larger holes there a likely hood of the bolts loosening and shearing from the play in the bolt holes.
The OEM plate is plenty strong for cars up into the 11-12 second range.

thanks that is exactly what he gave me.the red flag went up when i saw the different size holes.the converter holes match the oem plate holes ,so i will stick with that.

Make sure to locktite the bolts.

An SFI plate ? .. the only ones I have seen with that rating have had both TC bolt hole patterns.