853's
 

are they beter than stock 98 heads.Got them off Ebay for $100.00.

If so it is meaningless improvements. But they are a good base for porting.

according the book I have, the 853 was used from 97-00. So you may be replacing 853 heads with 853 heads...only difference being the valve cover bolt pattern

853's are defiently earlier i believe 99-00 just took them off my car
thought 00's had better heads guess not , i never looked at the number till then

Some of the '00 cars got the "better" 241 heads.

98-99's got 801 heads. Don't know if they flow any different. Bolt patterns are different on 00-02 heads than 98-99 heads.

????????

97 to 98 used the perimeter bolt valve cover and 99 and up used the center bolt valve cover. All the heads are interchangable on the block, just have to have the proper valve covers.

I believe the 243's started around mid 2000.

243's are LS6 castings.

i think i so an article in a magazine saing there is a difference in flow betuine years and heads!!!

In stock form, yes; but once ported they can all perform the same.
01/02 f-body 241 castings in stock form flow a little better than 853.

Oh yea, meant 241's